Issues with Storyline numerical calculations

Hi, I have prepared a Storyline to act as an online form, but am having a couple of problems with it. On one of the screens, the viewer has to input three numbers. These are then added together, with the final number being multipled by 2, and the result is displayed on the next screen. The problem is that it seems to work ok when I trial inputting low num bers, but not when the three numbers are over 100, which they often will be in a real scenario. I'm also having problems with the numerical entry boxes displaying the default value of 0, no matter how many times I delete and remake them. Would be very grateful for any help. 

Anne