Question

You were charged $51.50 last month for data usage on your smartphone. Your data plan charges a monthly fee of $20 plus $2.50 for each extra gigabyte (GB) used. How many extra gigabytes did you use last month?

Answer 1

He went 13 gigabytes over his limit
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Answer 2

20 + 2.5g = 51.50
2.5g = 51.50 - 20
2.5g = 31.50
g = 31.50 / 2.5
g = 12.6 <=== there were 12.6 extra gigabites used