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Hydrocarbons- homework help

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here, you are told that pentadecane is cracked to form octane, propene and ethane.
cracking is thermal decomposition, with one reactant and more than one product.

pentadecane is on the left, while the products octane, propene and ethene are on the right. this gives:

pentadecane → octane + propene + ethene [not ethane- that would be C2H6]

the formulae given to you in the question give the (unbalanced!) symbol equation:
C15H32 → C8H18 + C3H6 [not H8, that would be propane] + C2H4

C8 + C3 + C2 → C13, while C8 + C3 + 2C2 → C15
H18 + H6 + 2H4 → H18 + H6 + H8 → H32

therefore, the equation is C15H32 → C8H18 + C3H6 + C2H4