In these questions, when there's no actual numbers, they want you to express w in terms of other unknowns. Therefore, the procedure is to Isolate w.
k = (2b - 5w) / 3k
Do it normally like how you would do in algebra equations, Shift all the other numbers and unknowns which are on the side of w away until only w is left there.
So with this equation, first thing we would like to shift /3k away, so Shift this whole thing to the other side and turn it into x3k.
k x 3k = 2b - 5w
k x k equals to k^2,
So we can write this
3k^2 = 2b - 5w
Now Shift 2b to the other side too, and Change it into - 2b.
3k^2 - 2b = -5w
Last step, Shift x-5 to the other side, turning it into /-5.
(3k^2 - 2b) / -5 = w
Swap places and you'll get w = (3k^2 - 2b) / -5, so the answer is A.