In this case, we'll have to carry out several steps to find the solution.
Step 01:
Data:
$67.50 per month
$4 per gigabyte
total bill = $71.90 per month
g = ?
Step 02:
67.50 + g * 4 = 71.90
4g = 71.90 - 67.50
g = (71.90 - 67.50) / 4
g = 1.1
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