How to string together...?

I wrote a program to measure my reactor (Tekkit main) and I'm trying to do this

mon.write(waste + " MB") to string together waste amount, and the text MB, but it gives me an error,

So I did this:

mon.write(waste and " MB"

Which should work, but now it doesn't display the waste value, just the text MB

The concatenation operator in Lua is `..`, so:

mon.write(waste.." mB")