Ratio Formula Help!

[Torizcells]

Hello and thank you in advance for any help!

I am working on a spreadsheet someone created that has the below formula: 

=AA4*4.5-Z4 

Actual numbers= 10*4.5-34 

This formula is being used to show how many it will take to get to 4.5 

My problem: I need to change from 4.5 to 2.0 

When I change to this formula: 

AA4*2.0-Z4 I keep getting a negative number 

What am I doing wrong? What formula should I use if this one won't work? 

[#2]

@Torizcells

You probably won't get an answer because your question is not clear.

Please note that Excel takes into account the dot before dash calculation. So when you write:

=10*4.5-34
the same as:
=(10*4.5)-34
is
=45-34 = 11

In your second example, this is what comes out:

=10*2-34
is
=20-34 = -14

 The note: "This formula is being used to show how many it will take to get to 4.5" is not comprehensible to me. Please explain exactly what your formula is supposed to calculate.