Let x = John's age now
half of what johns age was 4 years ago: (1/2)(x-4)
is equal to one third of what it will be in 5 years time: (1/3)(x+5)
(1/2)(x-4) = (1/3)(x+5)
3(x-4) = 2(x+5)
3x - 12 = 2x + 10
The answer is (1+0.18)16.
