Storyline Variables that build on each other

I am trying to build an example where the user enters a value - example $1.00 on one slide, and on the next slide that $1.00 shows up and there is another input value of $2, and is added into a total of $3 on the second slide. Not sure if i can change an input value to a set value and still have it add? Added my image of how many different inputs I will need. My goal is that they have the interaction of adding cost - then hearing about the cost, then adding the next cost to see the value build. 

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