Question 502·Medium·Algebra

The line crosses the vertical axis at $(0,50)$. That means revenue is $50 when zero tickets have been sold. In slope-intercept form $y=mx+b$, $b$ is the value when $x=0$, so $y=mx+50$. The $50$ is the starting value, not the amount earned per ticket.

The labeled points $(4,110)$ and $(14,260)$ give two changes you can compare. The slope is the change in revenue divided by the change in tickets, so type $\frac{260-110}{14-4}$ in Desmos. It prints $15$, meaning revenue rises by $15 per ticket. Keep the point order the same in the numerator and denominator; don't count boxes on axes with different scales.

Put the per-ticket increase in front of $x$ and the starting revenue after it: $y=15x+50$. This gives the total revenue, in dollars, from selling $x$ tickets. Choice A.