12% of the Residents of One Town Are Aged Over

Short Answer

12% of the residents of one town are aged over 70. The distribution of sample proportions of samples of 210 residents is normal with a mean of 0.12 and a standard deviation of 0.022.
Suppose that you select a sample of 210 residents and find that the proportion aged over 70 in the sample is 0.09. What is the z-score corresponding to this sample proportion?