SAT Question 9c7741c6: Linear Equations In Two Variables answer and explanation with Desmos solution

It's given that Cameron drove $60$ miles per hour for $x$ hours; therefore, the distance driven at this speed can be represented by $60x$. He then drove $50$ miles per hour for $y$ hours; therefore, the distance driven at this speed can be represented by $50y$. Since Cameron drove $210$ total miles, the equation $60x+50y=210$ represents this situation. If $x=1$, substitution yields $60\times 1+50y=210$, or $60+50y=210$. Subtracting $60$ from both sides of this equation yields $50y=150$. Dividing both sides of this equation by $50$ yields $y=3$.