LUA If Statement

I was trying to use the LUA if function to represent the result with a “*” in front of the value under a circumstance using an if function.

C1      C2      C3
------------------
 2       5     *10
 3       5      15 

When the value in C1 is smaller than 3, the product of C1 and C2 needs to be shown as * with the actual product in C3. When the value in C1 is equal or greater than 3, the product of C1 and C2 is shown as 15. Could you please help me to find the if statement for this case?

Thank you!

Joy Li