A family of Microsoft spreadsheet software with tools for analyzing, charting, and communicating data.
Option 1:
Enter 80 in B15 and 100 in E15.
In F15, enter the formula =E15-B15.
Apply the custom number format
0 "mcfd"
To B15, E15, F15 and all other cells with similar data.
Option 2:
Enter the following formula in F15:
=SUBSTITUTE(E15, " mcfd", "")-SUBSTITUTE(B15, " mcfd", "")&" mcfd"