The function [tex]c(x)=72*(1.04)^x[/tex] models the cost in dollars, [tex]c[/tex], of 1 ounce of a certain chemical used in a laboratory. The variable [tex]x[/tex] represents the number of years since 2010.

a. Does the cost of the chemical increase or decrease over time? By what percentage per year does it do so?

b. How much does an ounce of the chemical cost in 2018? Round to the nearest cent.
Show your reasoning.