Write a linear equation for each of the problems below and solve it to find the required unknowns.
a) The perimeter of a rectangle is 180cm. If the length is twice the size of the width what are the dimensions of the rectangle?
b) A bill for $251.48 is made up of a $27.88 for materials and a fee per used time. if the hourly rate is $21.32, how many hours of work were done?