Macro: add x value to cellA and prompt to substract x to other cells

Hi there, i sure can use your help with this:
I have a value in cellA1(20)
I have values is cellB1(5),C1(5)D1(5) and E1(5)
CellF1 checks for A1-SUM(B1:E1)=0
I would like users to be able to clic on any B1 to E1 cell (through a button) and add a value (say:add 10 to D1)
The user then has to be prompted to substract a value of 10(or fractions of it up to 10) to cellB1, C1 or E1 so that my check F1 cell always remains 0. The user could decide to substract 5 from B1 and C1 or any combination that would substract and amount of 10 to the sum(B1:C1)

What macro can i put in my botton to get that result? Is it possible?

Thank you so much to this community.