I'm being fustrated by something that should be fair easy :/

In a spread sheet i've 3 columns 2 of text 1 of numbers. eg;

A B C
m op 10
t op 12
m op 22
m mac 33

what i'm after doing is adding up the qty in C when theres both m and op in a row.

If it was just 1 column it'd be a simple =sumif(a:a,"m",c:c), with using 'AND' i can compare idividual rows, but i can't seem to get it to add up over the entire range.