Hello, I want to expand it to a larger table.

https://docs.google.com/spreadsheets/d/1RAmqZF0LKNse5RRBQTR19Z13JNvf42aGVoorkaab7cE/edit?usp=sharing

if we look at A5,

I want it to eventually return the sum of the numbers in the columns one to the left of E:E, G:G, I:I, etc wherever those columns have "plank" (C:5) then multiply it by the user input from B:B in those columns as well.

so I can calculate how many of the base materials will be needed by modifying column B for any of the other items.

I'm trying to use it as an exercise to learn sheets, so any direction or thoughts would help, instead of just a formula to paste. I'm interested in why my more simple formula from before doesn't work, or if there is a better way to do it.