Can soapUI use math to add datagen results together?

Hi, 

I would like to generate some random numbers, and then add the results together to use in a later test step, but I don't know how to do it.

Scenario

I have a basket and have added an item for 3 GBP and and item for 5 GBP.  In the checkout test step, I will have to send the value 8 GBP to pay for the basket.  At the moment all of these values are hard coded, but I would like to use a datagen step to randomise the item prices, and then have soapUI calculate the result to use in another teststep.  Is this possible?

Many thanks

Amy