You collect stamps. You give steven 21 stamps. At the end youbhave 3. How many stamps did you start

You collect stamps. You give steven 21 stamps. At the end youbhave 3. How many stamps did you start with?

You start with s stamps.
s

You give Steven 21. Giving means you subtract from your total:
s - 21

You have 3 left
s - 21 = 3

To solve this equation for s, we type it in our math engine and we get:
s = 24