Question 30452
Let's call X to the number of video rentals you make.

If you go with the Big Video card, your total cost will be:
{{{Cost = 9.99 + 2.49X}}}

If you go with Main Street video card, your total cost will be:

{{{Cost = 20.49 + 1.79X}}}

So the system of equations is:
{{{Cost = 9.99 + 2.49X}}}
{{{Cost = 20.49 + 1.79X}}}

Substituting the 2nd equation into the 1st one, we get:

{{{9.99 + 2.49X = 20.49 + 1.79X}}}
{{{2.49X - 1.79X = 20.49 - 9.99}}}
{{{0.7X = 10.5}}}
{{{X = 10.5/0.7 = 15}}}

The cost will be the same after 15 video rentals.