Both T and D Flip Flops, if given an input signal frequency, they divide it by 2. It's called Frequency Division.
Given a series of T flip flops, since they toggle the input, in their output is actually the bit shifted to the right by one position. This is equivalent to performing a right shift, which in turn is equivalent to $ ÷ 2$
Since here we have a series of 3 T Flip Flops, the original input frequency would be divided by 2 thrice.
=> $\frac{100}{2*2*2}$
Option D