Help Needed for Forecasting / Predictions Formula

Dear All,

 

I'm currently analysing data for my School. I have two questions:

 

1) Is is possible to use forecasting formula on more than one set of data but view it all in one graph (whether that is as a number or %).

 

Please see the attached file.

 

2) Am I ok using Forecast Formula, or should I look for a non linear forecasting / predictions formula. If so which one?

 

Thank you in advance for any help & advice given.

 

Pete