Question 943305
A=assistant's charge; A+20=owner's charge 
12A+6(A+20)=$750
12A+6A+120=$750
18A+120=$750 Subtract 120 from each side
18A=630 Divide each side by 18
A=$35 ANSWER The assistant charges $35
Owner charges $20 more or $35+$20=$55
CHECK
12($35)+6($55)=$750
$420+$330=$750
$750=$750