Let

x = the present age of son, x>=0

y = the present age of father y>=0

Father is 4 times is as old as his son today means:

y = 4x

6 years ago, the product of the number denoting their ages was 252:

(x - 6)(y - 6) = 252

Plug y = 4x into the last equation:

(x - 6)(4x - 6) = 252

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click here to see the equation solved for x

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x = 12 years

y= 4*12 = 48 years

Father's present age is 48 years.

Son's present age is 12 years.