I have column A of cells containing three digit numbers in each cell.
In column B, I have the same thing cells with three digit numbers.
I would like to combine these two numbers into a six digit number.
How can this be done?

Also, in column B there are several cells with a zero value, so a blank is
displayed. How can I make the zero values into three digits or can I leave
the zero value as a blank and not affect the six digit number I want to
create?