The number of cakes needed for party, C, is dependent upon the number of guest at the party, G. Which equation shows the number of cakes as a function of the number of guests?

check above link.

graphically?   well, you graph them both, the solutions is where they both intersect each other, since there are two solutions, meaning they will meet twice, or namely the linear will run into the quadratic curve twice, and where they meet, those x,y coordinates are the solutions to the system.