Answer:
25
Step-by-step explanation:
Let x represent the son's age now. 5 years ago, it was x-5, and the father's age was (x -5)+25 = (x+20).
The product of their ages at that time was 900, so we have ...
(x -5)(x +20) = 900
x^2 +15x -100 = 900
x^2 +15x -1000 = 0 . . . . subtract 900
(x +40)(x -25) = 0 . . . . factor
x = -40 or +25 . . . . these values make the factors zero
The son's age now is 25.
