Answer:
4
Explanation:
The cost for plan 1 will be ...
p1 = 10 +5x
The cost for plan 2 will be ...
p2 = 30
These costs are equal when ...
p1 = p2
10 +5x = 30
5x = 20 . . . . . . . . subtract 10
x = 4 . . . . . . . . . . . divide by 5
The two plans will cost the same if a customer borrows 4 DVDs in a month.