System of linear equations

Question

A delivery truck is transporting boxes of two sizes: large and small. The combined weight of a large box and a small box is 90 pounds. The truck is transporting 60 large boxes and 70 small boxes. If the truck is carrying a total of 5700 pounds in boxes, how much does each type of box weigh?

Answer 1

L+S =90 multiply by 60, then subtract from the next equation

70L + 60S = 5700

60L + 60S = 5400

10L = 300 divide by 10

L = 30 pounds per large box

S = 90-30= 60 pounds per small box

70(30)+ 60(60) = 2100 + 3600= 5700