Number of multiples of 7 up to 1337: 
Number of multiples of 11 up to 1337:
Number of multiples of 77 up to 1337:
This means there are
distinct multiples of 7 *or* 11 up to 1337.
The sum of these multiples is
which can be computed using the well-known formula,
So you have
Number of multiples of 11 up to 1337:
Number of multiples of 77 up to 1337:
This means there are
The sum of these multiples is
which can be computed using the well-known formula,
So you have