In an electric circuit, two resistors with resistances x and y are connected in parallel. If R is the combined resistance of these two resistors, then the reciprocal of R is equal to the sum of the reciprocals of x and y. What is R if x is 4 Ohms and y is 6 Ohms?
Choose the correct answer:
A) 5 / 12  B) 7 / 12  C) 12 / 5  D) 7 / 5  E) 11 / 5

Rationale: "1 / r = 1 / x + 1 / y 1 / r = 1 / 4 + 1 / 6 = 5 / 12 r = 12 / 5 the answer is c ."
Answer: C