Two ways for the example posted:

You could try something like this:
=LEFT(I11,1)*I12
If 5mts is in I11 and 5 is in I12

You may also want to consider using a Custom Number format that would put
the mts into the cell instead of typing it manually.
Something like:
General"mts"

tj

"Malshenton" wrote:

any help to the above would be appreciated