Nima uses 2/3 cups of peanuts to make a recipe of 2 1/4 = 9/4 cups of trail mix. If we want to find how many cups of peanuts are there per cup of trail mix, we can do a rule of three:
If 9/4 cups of trail mix need 2/3 cups of peanuts, 1 cup of trail mix need X cups of peanuts:
since this is a triangle you would add up all the measure of this and set it equal to 180. 90 is the side with the box. so it would be 2x+15+x+90=180 then solve for x and you would get your answer.