I am confused in some of the questions. Could I have a little help?

Find the average rate of change for f(x) = x2 − 3x − 10 from x = −5 to x = 10.

What is the 12th term of b(n)=-4-2(n-1)

Afarmer has a large field that is x feet in length. he wants to fence in a rectangular section in the middle of the field , leaving a length of 100 feet of open field behind each end of the fenced rectangle.he also wants the width of the fenced-in space to be 100 feet less than its length. find the expressions to represent the length and width of the fenced section of the field