So you have .

The set of numbers is {41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63, 64, 65, 66, 67, 68, 69, 70, 71, 72, 73, 74, 75, 76, 77, 78, 79}.

When is divided by , the remainder is two, so . Thus with .

The set of numbers is {2, 7, 12, ... 47, 52, 57, 62, 67, 72, 77, ...}

When is divided by , the remainder is four, so . Thus with .

The set of numbers is {4, 11, 18, ... 46, 53, 60, 67, 74, ...}

Now intersect those three sets : which numbers are in all three of them ?

Our three sets are :

{41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63, 64, 65, 66, 67, 68, 69, 70, 71, 72, 73, 74, 75, 76, 77, 78, 79}

{2, 7, 12, ... 47, 52, 57, 62, 67, 72, 77, ...}

{4, 11, 18, ... 46, 53, 60, 67, 74, ...}

In red, the numbers that are in the first set.

And in blue, the number that is in all three sets.

Thus, .