The chemical equation would be:
2NO(g) + O2(g) --> 2NO2 (g)
At equilibrium state, the partial pressure of the gases would be as follows :
NO = 522 - 2x
O2 = 421 - x
NO2 = 2x
- - - - - - - - - - - - -
943 - x = 748
x = 195
Calculating for Kp,
Kp = (NO2)^2/ ((NO)^2 * (O2))
Kp = (2 * 195)^2/ ((522 - 2 * 195)^2 * (421 - 195))
Kp = 0.0386