SAT Question 81d0f1e6: Ratios Rates Proportional Relationships And Units answer and explanation with Desmos solution

It's given that the ratio $a$ to $b$ is equivalent to the ratio $63$ to $17$, or $\frac{a}{b}=\frac{63}{17}$. When $b=153$, the value of $a$ can be calculated by substituting $153$ for $b$ in the equation $\frac{a}{b}=\frac{63}{17}$, which yields $\frac{a}{153}=\frac{63}{17}$. Multiplying both sides of this equation by $153$ yields $a=567$. Thus, when $b=153$, the value of $a$ is $567$.