To find out how much each cupcake costs, let's first calculate the total cost of the cookies.
Jenny bought 6 cookies, each costing $1.50: \[ 6 \text{ cookies} \times 1.50 \text{ (per cookie)} = 9.00 \]
Now, we know the total cost that Jenny paid is $21. We can subtract the cost of the cookies from the total to find out how much she spent on cupcakes: \[ 21.00 - 9.00 = 12.00 \]
Now that we know she spent $12.00 on cupcakes, and since she bought 6 cupcakes, we can find the cost of each cupcake: \[ \frac{12.00}{6} = 2.00 \]
Therefore, each cupcake costs $2.00.