Double integration question

[ch1rontl34]

Hi everyone. I am trying to figure out how the Actex manual calculated a double integral. Can someone please walk me through how to integrate the following:

int(0,1) int(0,1) [e^[t1x1+t2x2]]dx1dx2

The solution says the answer is [[(e^t1)-1][(e^t2)-1]]/(t1t2)

Thanks for all your help and I hope you can understand everything in the format in which I've written it.

Btw this is number 22 on the chapter 8 practice problems on page 219 of the 2007 Actex Manual