data in user form. need help. want to have half populate and half entry data

pic attached. need first section of form to be ENTRY DATA...and then those numbers placed in c15, c16 and c19 only(upper left corner of excel worksheet)...the VOLUME, the RON, and the RVP. The MON is a fixed number. and once RON is entered, I need it to autofill the R+M/2 text box.


Then I need the cell references O24 - O28 to pass the data back to the bottom portion of form..i can figure the boxes out, but i need help with the code that does this.

PLEASE HELP..i really need to finish this and i am getting close. The code in there on right is incorrect.. i hust havent taken it out yet.

Thanks
PS WORD doc attached has two pics for help in understanding.

Easier to help if we can see the workbook with the user form.
Could you attach it?

BSB