Concept: The question tests on the basics of Algebra

Solution: 

 
1/3+1/4+1/5+1/6

=r (1/9+1/12+1/15+1/18)

=>1/3+1/4+1/5+1/6

=r1/3(1/3+1/4+1/5+1/6) (Taking the 1/3 common)

=>r1/3=1

=>r=3.r=3 (option c)