Answer:
4 GB
Explanation:
Let "g" represent the number of gigabytes of data used. Then the phone bill is computed as ...
bill = 65 + 12g
Aurora's bill is 113, so we can put that value into the equation and solve for g.
113 = 65 + 12g
48 = 12g . . . . . . subtract 65 from both sides of the equation
4 = g . . . . . . . . . divide both sides of the equation by 12
Aurora used 4 gigabytes of data in September.
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You can also use your mathematical reasoning to solve this problem. The total bill consists of two charges: a fixed charge of 65 and a charge that depends on data. If you subtract the fixed charge from the bill, you find that the charge that depends on data is 113-65 = 48.
The data charge is 12 times the number of gigabytes. The data charge on the bill is 48, which is 12 times 4. Then the number of gigabytes is 4.