looking for help with following

a1 b1 c1
x r m
x s m
t r m
x r d
y r m

The problem is I want to count the occurences of m
if (a1 = x and b1 = r) and if (a1 = y and b1 =r)
the solution I am looking for is ( 2 in the above table)
I have about 500 lines of data to process
* note ( range of a1 cell are merged ,ie: a1+a2 a3+a4 ect..)

any solution would be helpful.