Write the equilibrium-constant, kp, expression for the reaction a(g)+4b(l)< > 3c(g)+d(g)

When Kp = (the partial pressure of the products raised to exponents equal to their respective coefficients in the equation) / (the partial pressure of the reactants raised to exponents equal to their respective coefficients in the equation).
Kp = [P(C)]^3] * [P(d)] / [P(A)]
we here neglected the B as it is in liquid state.and we here deal with gas states only.
So your final answer is Kp= [P(c)^3]*[P(d)]/[(p(A)]