Answer: 21 cupcakes
Step-by-step explanation: x is the number of cupcakes. since she baked 45 cupcakes on tuesday, which is 3 more than 2x the number of cupcakes on monday, we would write 45=2x+3. First, subtract the 3 from both sides of the equation. This will give you 42=2x. Then divide both sides by 2. This will give you 21=x. So, the answer is 21