Given cos a = .23 find angle a in radians.

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?

Ineed if you could explain and give me the answer you! this needs done

Find the roots of the polynomial function f(x) = x^3 + 2x^2 + x