Find the number of 2 3/4 gallon cans which can be filled from a tank containing 90 3/4 gallons of oil?

The easiest way would be to convert the fractions to decimals.
2 3/4 = 2.75 and 90 3/4 = 90.75
So we have to calculate 90.75 / 2.75 = 33 2.75 gallon cans can be filled.

Let's make the base salary equal to x.
1) x + 10y = 1250   (base salary+ 10 hours of working = $1250 total we receive)2) x + 20y = 1400   (base salary+ 20 hours of working = $1400 total we receive)
Solve for y,
Once you obtain your y-value substitute it back into one of the beginning equations to find your x value.