the assistant can type 55 words in 1 minute
55 words m minutes
------------- x ---------------- =
1 minute 1
The minutes units cancel and you are left with only words
55 times m is 55m
1 times 1 is 1
55m/1 is the same as 55m and your units will be words
You don't have a value for m but if you did you could put that in. Say it was 3 minutes
55*3=165 words