Which value of x makes the quotient of (5x^5+90x^2-135x)/(x+10) undefined?

Dylan and dusty plan to take weekly surfing lessons together. if the 2-hour lessons are $20 per person and they plan to spend $100 each on new surfboards, what is the maximum number of lessons the two can take if the total amount spent for lessons and surfboards is at most $480?

How do you solve a question like this?

Simplify. (-2)^-3 a. -8 b. -1/8 c. 1/8 d. 8