The topic is circular measure

I have included one possible working below. There is another way, but using integration.

On a coordinate axes, we can set two random points such as (0, 0) and (14, 0) to denote the centres of the two circles.

Suppose the circle with centre (0, 0) has radius 12 cm and the circle with centre (14, 0) has radius 10 cm.

Letting 1 cm = 1 unit, the equations of our two circles would be

x² + y² = 144
(x - 14)² + y² = 100

We will only consider the portion of the graph above the y-axis for simplicity.

What we need to do here is to find the x-coordinate of intersection of the two circles and then perform integration on the curves using upper and lower limits (you can plot the graphs on Desmos for a rough idea). The integrals might get difficult to integrate though.

I will let you consider this alternative idea on your own for the time being.

Thank you so much!