How can I solve these problems? Please if u can, add an explanation, I would love to learn how ^_^

How to write 3 tenths and 5 tenths as a decimal

Sketch one cycle if the cosine function y=2cos2theta

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