C, the statements are sufficient together.

by statement (1), we know that 38 people of the 48 who have patios do not have swimming pools, it means that 10 have both. by statement (2), we know that the number of people who have neither is 10 also. this, we have accounted for everyone except those with only a swimming pool. this can just be the leftover people then. we know about 58 people so far, so it must be that 78 - 58 = 20 have pools but no patio. then we can see that the people with swimming pools are the sum of people with swimming pools only and the people who have both swimming pools and patios, which is 30