A phone company offers two monthly plans. Plan A costs $24 plus an additional $0.09 for each minute of calls. Plan B costs $20 plus an additional $0.14 for each minute of calls. For what amount of calling do the plans equal the same cost? What is the cost when the two plans cost the same?

x = number of minutes used, y = total cost in dollars

Plan A: y = 0.09x + 24

Plan B: y = 0.14x + 20

Equate the two right hand side (RHS) expressions and solve for x

0.14x + 20 = 0.09x + 24

0.14x - 0.09x = 24 - 20

0.05x = 4

x = 4/0.05

x = 80

The two plans will cost the same amount of money if you use up 80 minutes

Plug in x = 80 into either equation to find y

y = 0.09*x + 24

y = 0.09*80 + 24

y = 31.20

or

y = 0.14*x + 20

y = 0.14*80 + 20

y = 31.20

So both plans will cost $31.20 if you use up 80 minutes