Answer:
She can use under 5 gigabytes per month.
Explanation:
fixed charge: 60
charge per gigabyte: 3
charge for g gigabytes: 3g
total charge: 3g + 60
maximum amount to spend: under 75
3g + 60 < 75
Subtract 60 from both sides.
3g < 15
Divide both sides by 3.
g < 5
She can use under 5 gigabytes per month.