$T_{data\_transfer\_rate}$ $ = Track\_Capacity \times R\\ =300 \times 20\\ =6000\ \ words/sec$
Time req. to transfer 100 word block:
$T_{overhead}$ $ = \frac{100}{6000}\\ =0.01667 \ \ sec\\ =16.67 \ \ msec$
$T_{rotational\_delay}$ $ = \frac{1}{2} \times \frac{1}{20}\\ =0.025 \ \ sec\\ =25 \ \ msec$
Total time req. to acces one block:
$T$ $ = T_{seek\_time} + T_{rotational\_dealy} +T_{overhead}\\ =20 + 25+16.67\\ = 61.67 \ \ msec$
So, answer is option D