It tells me the answer but i need work, i don't get how to do it plzz and u it's case 5

Choose the triangle with x equal to 17.

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

Abox contains 1 plain pencil and 4 pens. a second box contains 5 color pencils and 5 crayons. one item from each box is chosen at random. what is the probability that a plain pencil from the first box and a color pencil from the second box are selected? write your answer as a fraction in simplest form.