Let students who do only backstroke = b
Let student who do only crawl = c
Let student who do both = x
Given that b + c + x =120 and c = 30
b + x = 120 - c = 120 - 30 =90
Find x
Statement 1 => of the 120 members... 72 do not swim and crawl this means b = 72
b + x = 90 ; x = 90 - 6 ; x = 90 - 72 ; x = 18, statement 1 is SUFFICIENT
Statement 2 => A total of 48 members swim the crawl .
Since this also includes those that do both crawl and backstroke
c + x = 48 where c = 30
30 + x = 48 ; x = 48 - 30
x = 18
Statement 2 is also SUFFICIENT
Since both statement alone are SUFFICIENT
Answer = option D