Explanation:

question is { 6,9,18}
3*2=6 , 3*3=9 ,3*6=18 we are seeing that by multiplying by 2,3 and 6 we get the desired numbers ,we have to find out that particular set
of numbers in which by multiplying by 2,3 and 6 we get that set of numbers.
in option A {14,21,42} we get these set of numbers by ; 7*2=14, 7*3=21 , 7*6=42 hence our option A will be correct.