We need not consider sector number. And multiplying sector number with rotational latency will not give us the worst case rotational delay. (I meant the one highlighted here 99( 0.2 ms +99*0.2 ms))
The question does not specify the track number, so we take average rotational delay = R/2.
We have 99 seeks (for tracks from 0 to 99), seek time = 99 * 0.2 ms = 19.8 ms = 0.0198 s
Each of the 100 track requests (0 to 99) will have some rotational delay. We take average rotational delay here as we are not provided with the information about the sectors.
Rotational delay = 100 * R/2 = 100 * 10 ms = 1 s
Total delay in servicing all 100 requests = 0.0198 s + 1 s = 1.0198 s
You can actually argue and take full rotational delay(=R) instead of average(=R/2), because in the worst case we will have to rotate the disk completely for each track request. In that case the answer would be 2.0198s. (There is a lot of discussion about this in the previous comments. I am not sure what to consider. If asked in exam my answer would be 2.0198s :P)