Answer:
We have the constraint 12x + 8y = 1800 to solve
x and y both have to be positive (she can't work negative hours)
If we choose x = 100 then we have 1200 + 8y = 1800
8y = 1800 - 1200 = 600
y = 75
We know this works because 12 * 100 + 75 * 8 = 1800 which is what she needs.
