Can someone please help me with this

Given f(x) = 17-x^2what is the average rate of change in f(x) over the interval [1, 5]?

Kapil needed to buy a long wooden beam. he went to two sawmills that each charge an initial fee plus an additional fee for each meter of wood. the following equation gives the price (in dollars) of a wooden beam from the first sawmill as a function of its length (in meters). p = 5+20xp=5+20x

Explain how you can show five less than a number using algebraic expression