SAT Question ebd457f4: Linear Functions answer and explanation with Desmos solution

It's given that Brian saves $\frac{2}{5}$ of the $$215$ he earns each week from his job. Therefore, Brian saves \left( \frac{2}{5} \right) \left( \ 215 \right), or \$$86, per week. If Brian continues to save at this rate of $$86$ per week for $9$ weeks, then he will save a total of $\left(9\right)\left(86\right)$, or $774$, dollars.