Help with statistics, please?

A study is done on giving men with osteoporosis human growth hormone with calcium and vitamin D3. This is thought to halt the fall in bone density and help build bone density. Bone density was measured by a continuous Z-score. The study contains a total of 100 patients and is designed so that alpha=0.05, and beta=0.8 for an effect size in which Z changes by 1.5 units between the treatment and the placebo groups. How many patients would they need in the study to make beta=0.8 for change of 0.5 units in Z?

Thank you!