Silicon dioxide reacts with carbon to form silicon carbide and carbon monoxide as shown in the unbalanced reaction below. Determine the percent yield of silicon carbide if 79.1 grams of carbon reacts with an excess of silicon dioxide and 67.4 g of silicon carbide is actually recovered.

SiO2 + C → SiC + CO. I’m working on this problem and I can not figure out where they got the 3 from