Solution
= Solution
The <interaction term> estimates that the weight-associated change in mean <testosterone> concentration is \b[$0.40688\,\mathrm{ng/dL}$ per gram greater in males than females]: the female slope is $-0.04518$ and the male slope is $-0.04518+0.40688=0.36170\,\mathrm{ng/dL}$ per gram.