Calculating Fluoride in toothpaste
Working with your numbers gives me the same result through moles of $\ce{NaF}$.  However, at this point you can multiply by the molar mass of fluoride, 18.998 g/mol, to get grams of fluoride, not moles, specifically, 0.0002835 g $\ce{NaF}$.

Parts per million is a mass-based concentration measure.  It's similar in concept to percent mass, but instead of parts per hundred, it uses parts per million.  Since we know the original mass of this sample, we can calculate the concentration in ppm based on that value.  It will be the same concentration as in the larger sample.

I get the following:
$\frac{0.0002835 \textrm{ g } \ce{F-}}{0.7540 \textrm{ g toothpaste}}\times 1000000 = 376.0\textrm{ ppm }\ce{F-}$