What is a trinomial in a problem

A polynomial with three terms is called a trinomial. Trinomials often but not always! have the form x2 + bx + c. At first glance, it may seem difficult to factor trinomials, but you can take advantage of some interesting mathematical patterns to factor even the most difficult-looking trinomials.

It’s a lot but hopefully I help:)

The answer is $9.90 with rounding to the nearest tenth