Solve ln y = kt for y

Do you mean solve

(In) (y) = (k) (t) for y?

If so then all you do is divided (In) on both sides and you'll get

Y = (k) (t) / (In)

The basic thing you need to know when solving for a variable is that you want to make it isolated.

On the other-hand, if you meant how do you solve for y = (k) (t) for y, then it's already solved.

Y is already solved because y=kt