2021 AMC 10B Problem 7

On one side of $\ell,$ circles tangent at $A$ are nested. For nested circles with radii $r_1>r_2>\cdots,$ the points inside exactly one of those circles have area $\pi(r_1^2-r_2^2)$ if there are at least two circles; a third smaller nested circle does not count because its points are inside three circles, not exactly one. To maximize the area, put the circle of radius $7$ alone on one side, and put the circles of radii $5,3,1$ on the other side. This gives $$\begin{aligned} &7^2\pi+(5^2-3^2)\pi \\ &=49\pi+16\pi=65\pi. \end{aligned}$$ Thus, the answer is D .