x = rate of mechanic who worked 5 hours
y = rate of mechanic who worked 15 hours
x + y = 200
5x + 15y = 1950
you find the first variable in one of the equations, then subsitute the result into the other equation. your answer would be:
the mechanic who worked for 5 hours charged $105 per hour, the one who worked 15 hours charged $95 per hour.
hope this helps :)