SOLUTION
From the question
The truck is transporting large boxes and small boxes
Let the weight of one large box be L
and let the weight of one small box be s
We are told that the combine weight of large box and small box is 55, that is

Also the truck is transporting 55 large boxes and 70 small boxes. And both totaling 3250 pounds
That is

Solving the equations simultaneously we have

Substituting the value of L for 55 - s into equation 2, we have

Hence Small box weights 15 pounds
Substituting the value of 15 for s in equation 1, we have

Hence Large box weighs 40 pounds