Choose from different balances in VBA

Hello All,

What is the best way to code the following

textbox1 shows the remaining hours of box1 [i.e. 48]
textbox2 shows the remaining hours of box2 [i.e. 32]
textbox3 shows the remaining hours of box3 [i.e. 8.5]

The user can put a number of hours in textbox4 that need to be extracted from the above boxes.

First box1 needs to be empties then 2 then 3.

So if the user puts 100 in textbox4 the new values will be as follows:

textbox1 shows the remaining hours of box1 [i.e. 0]
textbox2 shows the remaining hours of box2 [i.e. 0]
textbox3 shows the remaining hours of box3 [i.e. -11.5]

if the user puts 50 in textbox4 the new values will be as follows:

textbox1 shows the remaining hours of box1 [i.e. 0]
textbox2 shows the remaining hours of box2 [i.e. 30]
textbox3 shows the remaining hours of box3 [i.e. 8,5]

etc.

the 3 new values will be stored on sheet1 in column K below each other
Sheets("sheet1").Range("K" & LastRow).Value =
Sheets("sheet1").Range("K" & LastRow).Value =
Sheets("sheet1").Range("K" & LastRow).Value =

Any ideas?