Simplfy 21mm/7n

Question

when i tried doing this i got 3mmn or 3m^2n 

but the answers say it is 3m 

how do I solve this? 

Answer 1

If the answers say that it's 3m, then they're acting as if the numerator is 7m, not 7n.  Are you sure you're reading it right?  Maybe there's an error in the printing?