Let number of hours needed to work = x
Multiply number of hours by rate: 15x
Add what you already have saved:
15x + 215
This needs to equal at least 800:
The equation becomes:
15x + 215 >= 800
Solve for x:
15x + 215 >= 800
Subtract 215 from both sides
15x >= 585
Divide both sides by 15
X >= 39
They have to work at least 39 hours.