Answer:
$110
Step-by-step explanation:
Let a, b, and c represent the earnings of Alan, Bob, and Charles. The problem statement tells us ...
a + b + c = 480 . . . . . . the combined total of their earnings
-a + b = 40 . . . . . . . . . . Bob earned 40 more than Alan
2a - c = 0 . . . . . . . . . . . Charles earned twice as much as Alan
Adding the first and third equations, we get ...
(a + b + c) + (2a - c) = (480) + (0)
3a + b = 480
Subtracting the second equation gives ...
(3a +b) - (-a +b) = (480) -(40)
4a = 440 . . . . . . . . simplify
a = 110 . . . . . . . . . . divide by the coefficient of a
Alan earned $110.
_____
<em>Check</em>
Bob earned $40 more, so $150. Charles earned twice as much, so $220.
The total is then $110 +150 +220 = $480 . . . . as required
