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
[tex]L+s=55.............equation1[/tex]Also the truck is transporting 55 large boxes and 70 small boxes. And both totaling 3250 pounds
That is
[tex]55L+70s=3250[/tex]Solving the equations simultaneously we have
[tex]\begin{gathered} L+s=55 \\ 55L+70s=3250 \\ Making\text{ L the subject in equation 1, we have } \\ L=55-s \end{gathered}[/tex]Substituting the value of L for 55 - s into equation 2, we have
[tex]\begin{gathered} 55L+70s=3250 \\ 55(55-s)+70s=3250 \\ 3025-55s+70s=3250 \\ collecting\text{ like terms } \\ 15s=3250-3025 \\ 15s=225 \\ s=\frac{225}{15} \\ s=15 \end{gathered}[/tex]Hence Small box weights 15 pounds
Substituting the value of 15 for s in equation 1, we have
[tex]\begin{gathered} L+s=55 \\ L+15=55 \\ L=55-15 \\ L=40 \end{gathered}[/tex]Hence Large box weighs 40 pounds