I am self-studying models for financial economics and encountered the following problem:
I don't see how the author can conclude that $\gamma = -0.62$. Let's rearrange the second to last equation: $$\gamma - r = -4(0.19 - r)$$ as
$$r = \frac{\gamma + 0.76}{5}.$$
If $\gamma = 0.62$, then $r = 0.276.$
If $\gamma = -0.62$, then $r = 0.028$, as the author states.
So I don't see how the author can conclude $\gamma = -0.62$ when letting $\gamma = 0.62$ does not contradict that $r \geq 0$.