Keep a variable between panel change

Hello,

 I have a 2d game with a few panels, that contain some menus but I'm more interested in resolving that transfer of values between 3 panels. I have a TOP PANEL that stays active all the time that has a text called INCOME (has a script). I have Panel 1 with some buttons and by pressing one of the buttons we go into Panel 2. In Panel 2 we have two Game Objects each one with it's own script that give some values over time. Those 2 values are summed together in the INCOME text script (which is a part of the top panel which is always active). While I'm in the Panel 2 the summed INCOME in the TOP PANEL runs as it is supposed to run, but the second I press return to go to Panel 1, the summed INCOME freezes. How can I transfer this Summed INCOME between Panel 2 and Panel 1? 

Thank you

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