Question 1150570
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The difference in their ages is 51-9 = 42 years.<br>
When the father is 4 times as old as his son, their ages will be 4x and x; the difference will be 3x.<br>
3x = 42
x = 42/3 = 14<br>
The father will be 4 times as old as his son when the son is x=14 and the father is 4x=56.<br>
Since the father is now 51, that will be 5 years from now.<br>