In what direction does the river flow to the mouth or to the source?

To solve the problem, you need to figure out what the source and mouth are.

The source is where the river originates.

The mouth is the place where the river ends, that is, it flows into another river, sea or ocean.

Also, rivers flow from top to bottom. That is why they flow into the sea (at zero altitude relative to its own).

From this we can easily answer that the river flows from source to mouth.