Final answer:
To find out Kayla's monthly allowance, we need to reverse the process and solve the equation x - 15 - 0.4x = 3. Simplifying the equation, we find that Kayla's monthly allowance is $30.
Step-by-step explanation:
To find out Kayla's monthly allowance, first, we need to reverse the process. If she had $3 left at the end of the month, we need to add all her expenses and savings to that amount. We know that she spends $15 at the movies and puts 40% of her allowance into savings. Let's assume her monthly allowance is x. So, the equation becomes:
x - 15 - 0.4x = 3
Simplifying the equation, we get:
0.6x - 15 = 3
0.6x = 18
x = 18 / 0.6
x = 30
Therefore, Kayla's monthly allowance is $30.