Calculate [H+] in 1.0 L of a solution that contains 0.200 M NH4F. For HF, Ka=7.2 x 10^-4 and for NH3, Kb=1.8 x 10^-5.

a) 6.3 x 10^-7 M b) 0.200 M c) 5.6 x 10^-6 M d) 2.1 x 10^-8 M e) 5.6 x 10^-10 M

I know how to find the [H+] for a salt that only has one acidic/or basic component but I don't know how to solve for a salt with two components that work against each other. Can someone help me?

Thanks