A phone company offers two monthly plans. Plan A costs $15 plus an additional $0.07 for each minute of calls. Plan B has no initial fee but costs $0.09 for each
minute of calls.
For what amount of calling do the two plans cost the
Same?
minutes
What is the cost when the two plans cost the same?

x = the number of minutes of calls

y = the total cost

Plan A:

y = 0.07x + 15      (costs $0.07 per minute of calls(x) plus a fee of $15)

Plan B:

y = 0.09x       (costs $0.09 per minute of calls(x) and has no initial fee)

Since you want to find when they cost the same for the same amount of minutes, you can set the equations equal to each other because they have the same cost

y = y

0.07x + 15 = 0.09x         To find x, isolate/get the variable "x" by itself in the equation. Subtract 0.07x on both sides to get "x" on one side

0.07x - 0.07x + 15 = 0.09x - 0.07x

15 = 0.02x        Divide 0.02 on both sides to get "x" by itself

750 = x

Now that you know x = 750, you can substitute/plug it into either equation to find y.

y = 0.09x    Plug in 750 into "x" since x = 750

y = 0.09(750)

y = 67.5  

y = 0.07x + 15        (proves they will cost the same)

y = 0.07(750) + 15

y = 52.5 + 15

y = 67.5

x = 750 minutes

y = $67.50

So both plans will have the same amount of minutes of 750 at the same cost of $67.50