Yes in case of cascading counter which is nothing but an standard asynchronous counter u can multiply individual mod values to get resultant mod value..
So let us see how it works as well..Here after the input signal goes through 1st counter which is a mod 2 counter , so f1 = finp / 2
Now this output works as an input signal for 2nd flip flop of counter which is mod 3
fout = f1 / 3
==> fout = finput / 6
So net result is that output frequency gets divided by 6 w.r.t input frequency.
Thus this is nothing but the mod value of counter..
Hence output frequency here = 6 MHz / 6
= 1 MHz
As a shortcut , if u r given 2 counters each of mod value m and n then frequency gets divided by mn as a whole..