He meant the same unit, not different units. 3x/90x= 0.03333, or about 3%. X here can be any unit, be it MT, kg or m.
Can't say much about the rest.
If it means anything, for most of my time in Engineering we only used kilograms. A tonne would have been 10^3 kg. The SI symbol for tonne is t, not MT, lower case letter not upper-case. I'm not familiar with the standard abbreviations for barbaric "English Units" are, but
according to wikipedia it's simply "ton".
I doubt MT is a proper way to write
any unit.