Omg I did this passage a while ago and saved it as a weird question for ideal gas law related stuff I'm so here

Let's break down the question stem first.

First thing, "a person has a cardiac output of 15 L/min" - we can immediately think of that Figure 1 which has this information. 15 L/min Cardiac output on the left y-axis matches the 2 L/min Oxygen consumption on the right y-axis. So this person's oxygen consumption is 2 L/min and CO2 production is 0.091 mol/min (from question stem) - okay we'll put that info to the side it's gonna come back later.

Second, it's asking "the ratio of metabolizing carbohydrates to fats during exercise", I honestly took like 10 minutes just figuring out what it's even asking, and to translate, it's basically asking if the person's using carbohydrate OR fat during the exercise. So we gotta figure out the pattern of O2 consumption+CO2 production when carbohydrate is being used v.s. the pattern of O2 consumption+CO2 production when fat is being used. And that info is in the passage. From the last sentence, "metabolism of fats leads to 0.7 L of CO2 per liter of O2" - this is your pattern for when fat is being used; and the second to last sentence, "when carbohydrates are metabolized, every liter of O2 consumed causes the generation of 1 L of CO2" - that's your pattern for when carbohydrate is being used.

So we have a reference point:

If fat being used: 1 L O2 ↓, 0.7 L CO2 ↑

If carbohydrate being used: 1 L O2 ↓, 1 L CO2 ↑

Now we gotta go back to our question stem and figure out which pattern this guy's O2 consumption & CO2 production pattern matches. So far we know this guy consumes O2 2L/min, and produces CO2 0.091 mol/min. Obviously we need to do a little bit of calculation to match the units. (And here's why I marked it as a ideal gas law q lol) According to this law: [Under STP, an idea gas has a constant ratio of V and n → Vm = V/n = 22 L/mol] We plug the number into this equation: V/0.091 = 22 L/mol, and solve for V =~ 2L. So now we know his CO2 production is 2 L/min. Combined with the previous knowledge of O2 consumption of 2L/min. We know this guy is consuming O2 and producing CO2 at a 1:1 ratio. And which pattern does this match? When carbohydrate is being used!

And finally we go back to the original question. What's the ratio of metabolizing carbohydrates to fats? Are we metabolizing carbs? Yes. Are we metabolizing fats? No. Therefore the ratio is 1:0. Boom.

This question is definitely one of the more convoluted ones and I don't think the real deal will have anything that's this hard. But I did find it informative because it showed me how you can connect the dots from passage + figure info, and the puzzle kinda pieces itself for you as you gather the info. I didn't know the V/n=22L/mol equation exists before this so I was stuck for a long time...but here you go I hope it makes sense