k=39 and d=3
(k+y)/(d+y)=4 using k and d given...
(39+y)/(3+y)=4 multiplying both sides by (3+y)
39+y=12+4y subtracting 4y from both sides
39-3y=12 subtracting 39 from both sides
-3y=-27 dividing both sides by -3
y=9
So in nine years Kevin will be four times as old as Daniel.
check...
(39+9)/(3+9)=4
48/12=4
4=4
