we can raise two equations with the statements
"there are 135 boxes in all", so large and small boxes sum 135
[tex]\begin{gathered} x+y=135 \\ \end{gathered}[/tex]where x are large and y small
"If the truck is carrying a total of 4975 lbs", so the total weight is 4975
[tex]55x+20y=4975[/tex]solve x from the first equation and replace on the second to find y
[tex]\begin{gathered} x+y=135 \\ x=135-y \end{gathered}[/tex]replacing:
[tex]\begin{gathered} 55x+20y=4975 \\ 55(135-y)+20y=4975 \\ 7425-55y+20y=4975 \\ -55y+20y=4975-7425 \\ -35y=-2450 \\ y=\frac{-2450}{-35} \\ y=70 \end{gathered}[/tex]so there are 70 small boxes, now replace y=70 on any equation to find x
[tex]\begin{gathered} x+y=135 \\ x+(70)=135 \\ x=65 \end{gathered}[/tex]and there are 65 large boxes
