Emily is entering a bicycle race for charity. Her mother pledges $0.20 for every 0.5 mile she bikes. If Emily bikes 16 miles, how much will her mother donate? (pls help )

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