How long did each mechanic work?

Question

Two mechanics worked on a car. The first mechanic charged $55

 per hour, and the second mechanic charged $90

 per hour. The mechanics worked for a combined total of 20

 hours, and together they charged a total of $1275.

Answer 1

x+y = 20

mechanic x charges $55 per hour, for 15 hours

mechanic y charges $90 per hour for 5 hours

55x+90y = 1275

11x +18y = 1275/5 = 255

11x + 11y = 11(20)= 220

7y =255-220= 35

y=35/7 = 5 hours at $90 per hour

x = 20-5=15 hours at $55 per hour

55(15)+90(5) = 825 +450 = 1275