The first piece of information given to us in this problem tells us the numerical difference between the number of hours Amber worked and the number of hours Chance worked. If Amber worked 15 more hours than Chance last month, then:
hAmber = hChance + 15
Check this expression with a numerical example. Pick any number of hours that Chance may have worked last month (say, 50). If Amber worked 15 more hours than Chance, then Amber would have worked 65 hours. If you plug in hAmber = 65 and hChance = 50, then the above expression works out, and you can be confident that you've written down the right equation.
The second piece of information given to us in this problem tells us the proportional difference between Amber's hours and Chance's hours. Specifically, Amber worked 6 hours for every 3 hours that Chance worked:
hAmber/6 = hChance/3
Multiply both sides by 6:
hAmber = 2hChance
At this point, you've got a system of two equations with two unknowns. Solve for the unknowns using any method you like. Best of luck!