Taylor's total bill was $58 so then i had to subtract the $40 monthly bill part to find how much extra money she paid because her call was over 200 minutes
58-40=18
Then I divide the $18 by $0.15 since the $18 is the total amount of each time she was charged $0.15 for going over 200 minutes
18÷0.15 = 120
120 is the amount of minutes she went over her 200 minute limit
