Answer: the minimum number of hours is 2
Step-by-step explanation:
Let x represent the number of hours that she must babysit.
In a given week, she can work a maximum of 11 total hours. If Charlotte worked 8 hours walking dogs, it means that
x + 8 ≤ 11
x ≤ 11 - 8
x ≤ 3
She makes $7 per hour babysitting and $9 per hour walking dogs. It means that if Charlotte worked 8 hours walking dogs and x hours babysitting in a week, her total earnings would be
(7 × x) + (8 × 9) = 7x + 72
She must earn at least $85. Therefore,
7x + 72 ≥ 85
7x ≥ 85 - 72
7x ≥ 13
x ≥ 13/7
x ≥ 1.86
Since it must be whole numbers, then
x ≥ 2
Therefore, the range of hours is
2 ≤ x ≤ 3
The minimum number of hours is 2