Hey there!!
The ratio radius is given as 3:7
... Let's take the first circle's radius as 3 and the radius of the second's circle as 7.
The formula for the circumference as 2π(radius)
The circumference of the first circle as 2π(3)
... 6π
The circumference of the second circle as 2π(7)
... 14π
Ratio = 6π:14π
... 3:7
Hence, the answer would be option (B)
Hope my answer helps!