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Write a polynomial for a third-degree polynomial with leading coefficient -4

Galen sold tickets of his church’s carnival for a total of $2,820. children’s tickets cost $3 each and adult tickets cost $5 each. the number of children’s tickets sold was 30 more than 3 times the number of adult tickets slod. how many children’s ticket and how many adult tickets did he sell?

Which equation results from adding the equations in this system? x+6y=9 and -x+2y=-15