You can put this solution on YOUR website! Let
Present age of Bill = x
Six year ago he was = x-6
Then
Bill was 1/4 of his present age
1/4x=x-6
x/4=x-6
x=4(x-6)
x=4x-24
x-4x=-24
-3x=-24
-3x/-3=-24/-3
x=8
Bill is 8 years old
Check
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Bill present age 8 years
Six years ago = 8-6 = 2 (which is 1/4 of 8)