What is 23 to the 4th power times 5

Does anyone know how to do geometryme with this problem

F(n + 1) = f(n) – 8. if f(1) = 100, what is f(6)?

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