n = number of hours.
$5 per hour, total = 5*n = $5n
Since $35 has been saved.
The amount saved plus the amount got from baby sitting should be greater or equal to the $90 cost.
5n + 35 ≥ 90
5n ≥ 90 -35
5n ≥ 55
n ≥ 55/5
n ≥ 11
So Rodney should baby sit for at least 11 hours, that is 11 and above.
