Answer:
4x +$8
Explanation:
You know that ...
cost of both orders = cost of first order + cost of second order
Subtracting the cost of the first order gives ...
cost of both orders - cost of first order = cost of second order
(7x +$13) -(3x +$5) = cost of second order
(7x -3x) +($13 -$5) = cost of second order
4x +$8 = cost of second order