HOW MANY MG OF C2H4 MUST BE USED TO PRODUCED 875J OF HEAT

Is this a combustion? some other reaction.

H rxn x (Y/28*moles C2H4) = 875
Hrxn is the heat of the reaction, however, that is done in the problem. Y = grams answer, 28 is the molar mass of C2H4 and moles = the coefficient of C2H4 in the equation.