Answer: 68y
There are infinitely many ways to answer this. All you need to do is pick your favorite number and then stick y at the end of it. The terms -5y and 68y are like terms because they have the same variable attached.
You can think of 68y-5y as having 68 yoyos and then subtracting off 5 yoyos to get 63 yoyos when all is said and done. In terms of algebra, we would write 68y-5y = 63y.