How do I get this equation (H2o+Co2)+(C3H) reflect on the products of conservation of mass? My teacher just said to mention the total number of atoms on each side so as to the number of carbons, hydrogens, and oxygens to be the exact same number on each side.

Check your equation. C3H doesn't exist. Could that be C3H8 (propane) or C3H6(propene) or C3H4 (propyne)

Sorry i typed it wrong, it would be (H2O+Co2)+(C3H8) what do you think the conservation of mass would be?

I'm assuming the equation you want (I think you made another typo) is

2C3H8 + 10O2 ==> 6CO2 + 8H2O
You have 6 C on both sides. (6 from 2C3H8 and 6 from 6CO2)
You have 16 H on both sides. (16 from 2C3H8 and 16 from 8H2O)
You have 20 O on both sides. (20 from 10O2 on left and 12 from 6CO2 + 8 from 8H2O on the right.