Answer:
The answer is in the explanation.
Step-by-step explanation:
The reaction you want to obtain is:
3C(s) + 4H₂(g) → C₃H₈(g)
The sum of 3(b) + 4(c):
3b. 3C(s) + 3O₂(g) → 3CO₂
4c. 4H₂(g) + 2O₂(g) → 4H₂O(l)
3C(s) + 4H₂(g) + 5O₂(g) → 3CO₂(g) + 4H₂O(l)
Now, this reaction -(a):
-a. 3CO₂(g) + 4H₂O(l) → C₃H₈(g) + 5O₂(g)
3C(s) + 4H₂(g) → C₃H₈(g)