SAT Question 9f70fd47: Linear Equations In Two Variables answer and explanation with Desmos solution

A y-intercept of a graph in the xy-plane is a point where the graph intersects the y-axis, which is a point with an x-coordinate of $0$. Substituting $0$ for $x$ in the given equation yields $\frac{3\left(0\right)}{7}=-\frac{5y}{9}+21$, or $0=-\frac{5y}{9}+21$. Subtracting $21$ from both sides of this equation yields $-21=-\frac{5y}{9}$. Multiplying both sides of this equation by $-9$ yields $189=5y$. Dividing both sides of this equation by $5$ yields $\frac{189}{5}=y$. Therefore, the y-coordinate of the y-intercept of the graph of the given equation in the xy-plane is $\frac{189}{5}$. Note that 189/5, 37.8, and 37.80 are examples of ways to enter a correct answer.