The WAIS is the most common IQ test. The scale of scores is approximately Normal with mean 100 and standard deviation 15.

People with WAIS scores below 70 are considered mentally retarded when, for example, applying for Social Security disability benefits.

What percent of adults are retarded by this criterion?i know $\displaystyle z = \frac{x-\mu}{\sigma} $

I am just not sure how to find this percent its asking for with only the given info.

Any help to get me started would be greatly appreciated

Thank you