Make changes to an Android application

I have an app, already made, and it does this: This is what the app does already: This is a very simple app, simple arithmetic: Interface should be as easy as possible to use. Ask for only necessary permissions. Compatible with android versions as many as possible. Design interface with care please. First screen should show a logo ([login to view URL], I will send file later, use mock until then), Welcome! text and two buttons. Label: Select: Button 1: Label = 5-6 Feeks Button 2: Label = 7-8 Feeks For button 1 (on click screen should be loaded and input textboxes should appear) -------Variables to be used in equation---- (I will denote them with symbol) a, b, c, d, e, f, g, h, j, k , l ------------------Input to be taken from user---- (Labels will be red color and input from user will be variable---- Optional input: Name: TextBox 1 Village: TextBox 2 District: TextBox 3 Mobile: TextBox 4 Required input DAS: a Plot Size (m2): b NDVI (Plot): c NDVI (Rich Strip): d Button 3: Label = Go! ------calculations start---- e= c/a f= 602.47 * (e)1.1348 g = d/c h = g*f j = (10 (h-f) * 1.8)/0.5 k = j/0.46 l = (k*b)/10000 ------print this---- Fert. N (Kg/ha) = j Urea (Kg/ha) = k Urea (Kg/plot) = l _______________Line should be here Details: Name: TextBox 1 Village: TextBox 2 District: TextBox 3 Mobile: TextBox 4 -----END of Program----- There should be option to save this output as text file anywhere on storage For Button 2, everything is similar, just values of some constants will change For variable f, if button 2 is clicked then value will be this f= 2581 * (e)1.4072 ---Everything else remains same----- __________________________________ What i need new: To add a main page screen, and add two buttons, button one should open the current main screen, and button two should open another newly added screen with a button, This button should do what the above button 1 does, just with different value of constant i.e. f variable and j variable. everything else remains same. I can provide you the source code also.