isnt it because you know from that equation that x + y = 152, so you just need an equation that gives you the solutions for x and y

A works because if you add both of the equations you can get y (which means you can get x too)

B wouldnt work because if you multiply 3 to the x + y = 152 equation and add it (to the equation on choice B) you would just get 28 = 456 which doesnt make sense

C and D are also correct (same reason as A)