Please go over steps in detail because I did not understant how other solutions arrived at the answer when there are two unknowns in the equation.

Currently, the expected return on the market portfolio $($Rm$)$ is $12\mathrm{.}3\%.$ The Goldman Sachs

Group's stock has a beta of $1\mathrm{.}44.$ The expected return of the stock based on the CAPM is $15\%.$

What is the risk$-$free rate?