A sample of toothpaste was analyzed for its fluoride content by treating a 250 mg sample with an ionic strength buffer to extract F- followed by dilution to 100.0 mL. The potential reading with a fluoride ISE was +150.3 mV. After addition of 10.0 mL of a 50.0 ppm Fstandard, the potential reading became +110.8 mV. Assuming a slope of -58.0 mV for the fluoride ISE, calculate the fluoride content of the toothpaste in %NaF.