If 500 ft of wire weighs 12lb, what will be the weight of 150ft of the same wire?

500ft of wire weighs 12lb

150ft of the same wire will weigh?

Cross multiplying gives:

(150ft × 12lb) ÷ 500ft

1800ft(lb) ÷ 500ft

= 3.6ft

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.