SAT Question 0231050d: Percentages answer and explanation with Desmos solution

The percent decrease between two values is found by dividing the difference between the two values by the original value and multiplying by $100$. The line graph shows that the annual snowfall in $2003$ was $40$ inches, and the annual snowfall in $2007$ was $10$ inches. Therefore, the percent decrease in the annual snowfall from $2003$ to $2007$ is $\left(\frac{40-10}{40}\right)\times 100$, or $75$. It's given that this is equivalent to $p\%$, so the value of $p$ is $75$.