#2m# means (#2xxm#)
One way to think of this is having
#color(white)("XXXX")#2 rows each with the same number of monkeys
#color(white)("XXXX")##color(white)("XXXX")#(we're not sure of the exact number of monkeys in each row,
#color(white)("XXXX")##color(white)("XXXX")#but we can see that there are the same number
#color(white)("XXXX")##color(white)("XXXX")#and for convenience we will call this number #m#)
Similarly #5m# means (#5xxm#)
And we can think of this in the same terms as #2m#
#color(white)("XXXX")#5 rows each with the same number of monkeys (and the same number of monkeys as in the 2 rows)
If we add 2 rows of monkeys and 5 rows of monkeys
we get 7 rows of monkeys (each row with #m# monkeys)
We can write this in symbols as
#color(white)("XXXX")##2m + 5m = 7m#
