Answer:
5 months
Step-by-step explanation:
Let n be the number of months.
1. Triax offers a new phone for $50 and a limited service for a monthly fee of $40. Then the phone will cost
$50+$40·n.
2. Cellular offers a new phone and unlimited service for a monthly fee of $50. Then the phone will cost
$50·n.
Equate these to amounts:
50+40n=50n,
50=50n-40n,
50=10n,
10n=50,
n=50:10,
n=5.