Chemistry energetics question

So i’ve tried to work this out by cancelling out the molecules we don’t need. For a) seeing as its enthaply of formation of methane i flipped the first equation so it gives a +890 and methane is on the left. I did the same to cancel the 1/2o2 and co2 but i’m stuck.

The process here is to construct the equation you need by adding and reversing the given equations. You do the same to the energy value and "hey presto" the answer.

So is you need the enthalpy of formation of methane you first write it out:

C(s) + 2H₂(g) ==> CH₄(g)

and now you construct that equation using the others.

C(s) appears in equation (3) so let's start there:
C(s) + O₂(g) ==> CO₂(g)

H2(g) appears in equation (4) so double (4) and add it to (3)

(5) C(s) + 2H₂(g) + 2O₂(g) ==> CO₂(g) + 2H₂O(l)

Now we need CH4(g) on the right hand side, so reverse equation (1) and add it to the result (5) above

C(s) + 2H₂(g) + 2O₂(g) ==> CO₂(g) + 2H₂O(l)
CO₂(g) + 2H₂O(l) ==> CH₄(g) + 2O₂(g)
----------------------------------------------------- add
C(s) + 2H₂(g) ==> CH₄(g)