Problem: Acetylene reacts with $O_2$ to give carbon dioxide and water vapor

$2C_2{H}_2(g)+5O_2(g)4C{O}_2(g)+2H_{2}O(g)$

If you mix $C_2{H}_2$ and $O_2$ in the correot stolichlometric ratio, and if the total pressure of the mixture is $140.mm$ Hg$,$ what are the partial pressures of the gases before the reaction occurs?