Your cereal has 10g of fiber, you add the soluble and the insoluble, assuming both are listed (normally just 'fiber' is listed).

A word of warning, though. Often the fiber has been pre-subtracted, meaning that the cereal has 38g of carbs of which 10g are fiber and 28g are 'effective carbs'. You can double check if this is the case by doing a little math. 1g of carbohydrate has 4 calories (as does 1g of protein). 1g of fat has 9 calories. All the grams of protein and carbs mutiplied by 4 plus all the fat grams x 9 should equal the same amount of calories as a serving. If there is a discrepancy it's usually because your fiber was pre-subtracted.

There is also a little tool under "LC Tools" up atop every page called the Hidden Carb Inspector you can use to do this.

HTH,
-Nat