setting a value to a variable and adding to the variable

I have a problem I can't figure out.

I have a numeric variable the user inputs data into and in a later slide I would like that variable to show up and then increase a couple of time first by 10 and then 15. I got this work somewhat by copying the variable in the timeline and adding triggers that increase the value when the object in the timeline ends. This worked ok unless the user replay the slide or clicks retry. The variable keeps adding value not to the original variable but to the most recent added on number. If you keep replaying the timeline the number grows without limit.

 

So is there a way to add only to the original variable?

like if Variable 1 = 50 can I make another Variable equal Variable 1 + 10?

by using multiple variables or multiple triggers maybe.

Thanks for any input on this, I've looking at it a dozen types of ways and can't come up with anything. 

 

I have the file attached if anybody has a second to help.

 

-C