Answer:
d = 55 boxes of deluxe
s = 135 - 55 = 80 boxes of standard
Step-by-step explanation:
This is a system of equations.
Let s = number of standard boxes
d = number of deluxe boxes
s + d = 135 sold
7s + 13d = $1275
we can use substitution
s = 135 - d
7*(135 - d) + 13 d = 1275
945 - 7d + 13d = 1275
6d = 330
d = 55 boxes of deluxe
s = 135 - 55 = 80 boxes of standard