well I need help... I have tried many times but can't figure this one out.

The waist measurement of students in a college is normally distributed. The standard deviation is known to be 5 inches. It is found that 15% of the students have waist sizes less than 28 inches. What proportion of students will have waits between 30 and 35 inches ?
A. 0.3795 b. 0.2389 c.0.1406 d.0.0983 e. none of the above

OK if 15% have less than 28 inches so the proportion lies on the 85% left which should be x>28. I'm stuck from here... help

Look up the z-score for .15. We see it is -1.04

Use z=\frac{x-{\mu}}{\sigma}

Now, solve: -1.04=\frac{28-{\mu}}{5} for {\mu}

That is the mean.

Then, you have what you need to find the percentage between 30 and 35 by using the same formula, finding the percentages and subtracting them.