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.