Question 100765
let x be the numer of years.
{{{(39+x)/(9+x)=3}}}
39+x=3(9+x) multiply both sides times the denominator.
39+x=27+3x 
2x=12 subtract x and 27 from each side.
x=6 divide 2 into each side.
Check:
39+6=45
9+6=15
45/15=3
Ed