Chapter 8 - Section 8.1 - The Square Root Property and Completing the Square - Exercise Set - Page 594: 78

$ 12.5$%

Since, $A=(1+r)^t$ Plug the values in the given expression. Such as $A=(1+r)^t$ or, $101250=80000(1+r)^2$ This implies that $r=\sqrt {\dfrac{101250}{80000}}-1$ or, $r=0.125$ and Hence, $r$ can be written as: $r = 12.5$%