Kristi’s cell phone company charges her a fixed monthly fee of $6.95 plus $0.07 per minute of service usage. If her bill last month was $18.15, how many minutes of cell service did Kristi use?
160 minutes.
The formula for Kristi's bill is (6.95 plus 0.07 per minute for a total of 18.15)
6.95 + 0.07m = 18.15
Subtract 6.95 from both sides
0.07m = 11.20
Divide both sides by 0.07
m = 11.20 / 0.07 = 160
So Kristi used 160 minutes.
