To find the cost of each cookie, we can start by setting up an equation based on the information provided.
- Let the cost of each cookie be \( x \).
- Ada buys one cake for $20.
- She buys four cookies, so the total cost for the cookies is \( 4x \).
- The total amount spent on the cake and cookies is $28.
We can set up the following equation:
\[ 20 + 4x = 28 \]
Now, we can solve for \( x \):
- Subtract 20 from both sides:
\[ 4x = 28 - 20 \]
\[ 4x = 8 \]
- Divide both sides by 4:
\[ x = \frac{8}{4} \]
\[ x = 2 \]
Thus, each cookie costs $2.