To determine the equation that represents the relationship between the cost of the cookies \( y \) and the number of cookies \( x \) during the sale, we need to calculate the price per cookie during the sale.
Originally, the baker charges $2.00 for 4 cookies. Therefore, the price per cookie is:
\[ \text{Price per cookie} = \frac{2.00}{4} = 0.50 \]
During the sale, the baker charges $0.10 less for each cookie:
\[ \text{Sale price per cookie} = 0.50 - 0.10 = 0.40 \]
The relationship between the total cost \( y \) and the number of cookies \( x \) is given by:
\[ y = 0.40x \]
Thus, the correct equation is:
\[ y = 0.40x \]
So, the appropriate response is:
y=0.40x