Since the intersection is - by definition - common to both sets, we can work out the number of people that use only the fitness suite or the swimming pool.
We know that 57 people use the fitness suite, but 36 of those are already counted in the intersection. So, 57-36=21 people use only the fitness suite.
The same goes for the swimming pool: 49-36=13 people use only the swimming pool.
So, we have:
21 people using fitness suite only
13 people using swimmng pool only
36 people using both
This sums to 21+13+36=70 people. We deduce that 30 people don't use any of the features.
