I need Help with Cell Formatting to be able to copy

there are 2 good options:

a) my preferenced is to NAME that 7% cell.  you can do that by clicking on the cell then clicking on the name of the cell to the left of the formula bar and typing a name:

 here is highlighted D10 and then highlighted the name to the left of the formula bar then typed a name for that cell: 

  alternatively you can go to Formulas -> Name Manager and add new name:

either way now when you use that name in a formula it won't change when copied so

=A4 - A4*Mpercent 

b) simply prefix the row/column that shouldn't change using $ so

= A4 - A4 * $D$4