I don't know how to do this can someone explain it

Two sides of a triangle mesure 20cm and 30cm. what is the measure of the third side

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

Analyze the diagram below and complete the instructions that follow. how to find tan