Hi, I need help please,

I have the following data:
A B
Month's Net Income $
Month's Total Expense 00
Total Revenue $
Percent Revenue

I would like to have my Percent Revenue % (B4) as result of my Income and
Expense. Also, I would like to have the percent (B4) showing negative percent
result as need it.

For instance, lets make a example, if I earn 50 dollars in my Income (B1) ,
but I spent 100 in (B2) I would like Percent Revenue (B4) show me -100%
otherwise, if I earn 100 and spent 50 it would show me %50

Please help me

Would anyone guide me please.