passing values between pages??

My project uses 2 pages MainPage.xaml and SecondPage.xaml. i have a textbox in MainPage.xaml which is used to enter numbers. i intend to perform calculations using the data entered in the first page and display results in SecondPage.xaml. But the problem is how do i pass a numbers to the second page from MainPage.xaml and use it for calculations in the SecondPage.xaml?? Please help