### how to get around white space problem

Here is the formula in column L:
=IF(ISBLANK(D5)," ",(G5+K5)+(G5+K5)*$M$3)

Column D is units; column G is the extension of E*F (qnty*cost); column K is tax; M3 is markup rate. Not every line item, or row, have ~~tax.~~tax; so K is sometimes white space.

This formula works in Open Office, Google spreadsheets, etc. But in Libre the answer is #VALUE!
I have replaced the commas with semi-colons but the program changes them back to commas.
I have replaced the blank (" ") with "0" (without quotes) but the answer is #VALUE!
I have added parenthesis to encompass the entire third set, as in ((G5+K5)+(G5+K5)*$M$3)).
Any help here? Thanks in advance.