Can someone please walk me through this?-- 25 pts! Calculate the change of enthalpy for the reaction CH4 (g) + NH3 (g) --> HCN (g) +3H2 (g) from the following reactions:

Reaction 1: N2 (g) + 3H2 (g) --> 2NH3 (g); Change in enthalpy(∆ H): -91.8 kJ/mol

Reaction 2: C (s, graphite) + 2H2 (g) --> CH4 (g); Change in enthalpy(∆ H): -74.9 kJ/mol

Reaction 3: H2 (g) + 2C (s, graphite) + N2 (g) --> 2HCN (g); Change in enthalpy(∆ H): +270.3 kJ/mol

I have to include the following:

>The numerical answer with correct units.

>State which reactions, if any, you had to "Flip". ("Flipping" refers to modifying one of the reactions above to make a chemical be present on the other side-- like flipping an N2 that is on the reaction side. If it needs to be on the product side, you flip the reaction. Hope that makes sense.)

>State which reactions you had to multiply, if any, to get the correct amount of the compound. Also, include how much you multiplied the reaction by.