Answer:
140 pounds
Step-by-step explanation:
let s == small box
m = medium box
= large box
the following 3 equations can be derived from the question
s + m = 20 equation 1
m + l = 28 equation 2
l + s = 24 equation 3
make m the subject of the formula in equation 1 and 2
m = 20 - s equation 4
m = 28 - l equation 5
equate equation 4 and 5
20 - s = 28 - l
l - s = 8 equation 6
solve equation 3 and 6 using simultaneous equation
l + s = 24 equation 3
l - s = 8 equation 6
subtract equation 6 from 3
2s = 16
s = 8
substitute for s in equation 1
8 + m = 20
m = 12
substitute for m in equation 2
12 + l = 28
l = 16
total weight = (4 x 8) + (5 x 12) + (16 x 3) = 140 pounds
