Which is equivalent to (-m)4x n2 ?

What is the size of the matrix resulting from

Kapil needed to buy a long wooden beam. he went to two sawmills that each charge an initial fee plus an additional fee for each meter of wood. the following equation gives the price (in dollars) of a wooden beam from the first sawmill as a function of its length (in meters). p = 5+20xp=5+20x

The perimeter of a rectangle is 42 inches. if the width of the rectangle is 6 inches, what is the length