Ps help. Many tks and God Bless:)

A shopkeeper bought x pencil cases for $108

(a) Write down an expression in terms of x, for the cost price, in dollars, of one pencil case

(b) the shopkeeper sold 10 pencil cases at a profit of $1.50 each and the remaining at $7.50 per pencil case. Write an expression in terms of x, for the total amount of money received from the sale of the pencil cases.

(c) Given that he made a profit of $12 from the sale, form an equation in x and show that it reduces to xsquared -24x +144=0. Hence find the number of pencil cases bought by the shopkeeper.