In this task, you need to answer the given multiple-choice question on geometry. Classify your answers into 'a', 'b', 'c', 'd', and 'e'.
Q: Problem: in an electric circuit , three resistors with resistances 2 ohms , 5 ohms and 6 ohms are connected in parallel . in this case , if r is the combined resistance of these three resistors , then the reciprocal of r is equal to the sum of the reciprocals resistors . what is r value ?
Options: ['a ) 13 / 15 ohms', 'b ) 15 / 13 ohms', 'c ) 5 / 8 ohms', 'd ) 3 / 7 ohms', 'e ) 45 / 18 ohms']
A:
a