# Deriving Marginal Product For Hecksher-Ohlin

I'm using the second edition of applied international trade by Bowen and for the HO model, the marginal product with respect to capital ought to be the first term of the final answer (as given in the textbook) but I'm unable to derive it.

I'm pretty sure I'm wrong somewhere as the final answer I derived is negative (average product > marginal product) but I can't figure out where I'm wrong.