ok so in this problem i have to solve for K to make the problem exact, that means My = Nx. so here is the problem.

(y^3 + kxy^4 - 2x)dx + (3xy^2 + 20x^2y^3)dy = 0

so My= 3y^2 + 4kxy^3 and Nx=3y^2+60x^2y^2

the answer in the book says 10, but i don't see how they got that from what i have k is not going to be a number.any help would be appreciated.

thanks in advance.