Question

With a platinum catalyst, ammonia will burn in oxygen to give nitric oxide, NO.
4 NH3(g) + 5 O2(g) 4 NO(g) + 6 H2O(g) ÄH = -906 kJ

What is the enthalpy change for the following reaction?
NO(g) + 3/2 H2O(g) NH3(g) + 5/4 O2(g)

Answer 1

I assume that ÄH is supposed to be "delta H"

Note that the second reaction is the reverse of the first, but with the number of moles reacting 4 times less.

That should give you a pretty good hint of what the answer is.