SAT Question 1fbd3b67: Percentages answer and explanation with Desmos solution

Choice B is correct. It's given that the number $b$ is $80\%$ less than $24$. It follows that $b$ is equal to $24$ minus $80\%$ of $24$, which can be written as $b=24-\left(\frac{80}{100}\right)24$. This is equivalent to $b=24-0.8\left(24\right)$, or $b=4.8$. It's also given that the number $a$ is $190\%$ greater than the number $b$. It follows that $a$ is equal to $b$ plus $190\%$ of $b$. Since $b=4.8$, this can be written as $a=4.8+\left(\frac{190}{100}\right)4.8$. This is equivalent to $a=4.8+1.9\left(4.8\right)$, or $a=13.92$.