(a) Linda bought x identical wooden rulers for $36. Write down an expression, in terms of x, for the cost of each ruler.
(b) A plastic ruler is 15 ¢ cheaper than a wooden ruler. Write down an expression, in terms of x, for the cost of plastic ruler.
(c) If Linda uses the same amount of money to buy plastic rulers instead, she will be able to buy 20 more plastic rulers. Form an equation in x and show that it reduces to x^2+20x-4800=0.
(d) Solve this equation to find the cost of each plastic ruler.