My understanding of this is as follows:
There are 8 people, 2 of which must sit together. So, we have 6 + 1(as one unit) =7
The 2 people can sit together in 2! ways. The remaining 6 can be seated in 6! ways without any restrictions.
So we have a total of: 2! x 6! =1,440 ways without any restrictions. But, we have a restriction that Rosa cannot sit on either side of Pierre and Thomas. Of the 6! ways that the 6 people can sit, Rosa sits to the left of Pierre and Thomas in 6!/6 = 120 ways. And, similarly, she can sit to the right of Pierre and Thomas in 6!/6 = 120 ways. So, 120 x 2 = 240 positions that must be excluded from 1,440. Or:
1,440 - 240 =1,200 ways that the 8 people can be seated on a round table with the restrictions given.