Question 106604
You've got the right idea, but...
Let x = the number of hours worked by the apprentice.
The plumber worked 3 hours more than that, so the plumber workrked (x+3) hours.
The plumber gets paid $28 per hour so he/she earns (x+3)($28) while the apprentice gets $15 per hour so he/she earns x($15).  The sum of these earnings is $213.  So here's the equation you need to solve for x:
(x+3)($28) + x($15) = $213 Simplify and solve for x.
28x + 84 + 15x = 213 Combine like-terms.
43x + 84 = 213 Subtract 84 from both sides.
43x = 129 Divide by 43
x = 3 This is the number of hours worked by the apprentice, and, at $15 per hour, he/she earns $45.
The plumber works x+3 hours or 6 hours, and, at $28 per hour, earns $168