Como se resuelve el siguiente problema, no entiendo porque el 2 va abajo?

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Solve for x and y: 217x + 131y = 913; 131x + 217y = 827

Which equation is y = -6x2 + 3x + 2 rewritten in vertex form?

The water company charges a residential customer $41 for the first 3,000 gallons of water used and $1 for every 200 gallons used over 3000 gallons. if the water bill was $58 how many gallons of water were usedanswersa 3400 gallonsb 6000 gallonsc 6400 gallons d 7000 gallons