Let x represent the number of hours that he spent washing cars.
Let y represent the number of hours that he spent landscaping.
In a week, he can work no more than 19 total hours. This means that
x + y ≤ 19- - - - - - - - - - - -1
Jacob is working two summer jobs, making $10 per hour washing cars and making $8 per hour landscaping. He must earn at least $170. This means that
10x + 8y ≥ 170 - - - - - - - - - -2
If Jacob worked 4 hours landscaping, it means that
x + 4 ≤ 19 x ≤ 19 - 4 x ≤ 15
Also, 10x + 8 × 4 ≥ 170 10x + 32 ≥ 170
10x ≥ 170 - 32 10x ≥ 138
10x ≥ 138/10 x ≥ 13.8
The minimum number of hours is 14
