How much fence would you need to replace the fence of a 30 foot by 40 foot playground? how much sod would you need to re-sod the lawn?

360 different combinations

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.