Is y=-x^3+2x linear or non linear

Ineed to learn how to solve this problem

Write two subtraction equations that are equivalent to 5 + 12 = 17.

Jamie went to home depot.she bought 25 bags of soil that cost $9 per bag.she bought 15 pots at $8 each,and she bought 23 bags of pebbles at $15 each.she used a coupon that gave her $5 off for every 100 dollars she spent.how much did jame pay at the end?