The Output Is the Total Cost of a Shirt, Where $y = 1.09 x$

The output is the total cost of a shirt, where x is the price of the shirt and a sales tax of 9% of the price is added. Write an equation describing the output (y) as a function of the input (x) .

A) $y = 1.09 x$
B) $y = x + 0.09$
C) $y = x - 0.09$
D) $y = 0.91 x$
E) $y = 0.09 x - 1$