Use substitution
Plug in 5x for y
5x = 2x - 15
Subtract 2x
3x = -15
Divide by 3
x = -5, y = -25
Solution: (-5, -25)
$70 = 270 min
x = 1260 min
Where x is the charge of phone service per 1260 min.
Cross multiply:
1260 * 70 = 270 * x
88200 = 270x
88200/270 = x
x = 326.67
The total charge of cellular phone service for 1260 min is $326.67
