Ann purchased a prepaid phone card for 20$. Long-distance calls cost 12 cents a minute using this card. Ann used her card only once to make a long-distance call. If the remaining credit on her card is 16.76$, how many minutes did her call last?

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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.