David's age: x
Joshua: x + 5
Simon: (x+5) + 4 or x + 9
Simon's age + David's age = 15
(x+9) + (x) = 15
2x = 15 - 9
2x/2 = 6/2
x = 3
The ages of the boys:
David: x = 3 years old
Joshua: 3+5 = 8 years old
Simon: 3+9 = 12 years old
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