A Compound Containing 3atoms Of Carbon & 8atoms Of Hydrogen Is Combined In A Reaction With Oxygen Molecules.The 2 End Products Of This Equation Are Carbon Dioxide &water.What Element Should You Look At 1st In Balancing This Equation?

The element you would look at first before balancing the equation would depend on you. If looking at the organic compound first makes it easier for you to balance, then why not. On the other hand if looking at Oxygen first gives you a clearer picture, then for sure, oxygen id the one to look at first.
 
Oxygen has the higher number of molecules in the balanced equation. 5
 
C3H8 + 5O2 = 3CO2 + 4H2O