running number in a cell every time click 'keep' button.

pls help me make a running number in b12 after clicking the "simpan" button. the function of the 'simpan' button is to to update the screen. and automatically copy things written in the form into selected sheet. the details would be copied into selected sheet which is by selecting the sheet name in sheet1,c10.

i also attached the sample of my work. its already coded.
pls lend me a time to at the workbook.