A satellite is composed of 24 modular units, each of which is equipped with a set of sensors, some of which have been upgraded. Each unit contains the same number of non-upgraded sensors. If the number of non-upgraded sensors on one unit is 1/6 the total number of upgraded sensors on the entire satellite, what fraction of the sensors on the satellite have been upgraded? Choose the most appropriate option.
A) 5 / 6  B) 1 / 5  C) 1 / 6  D) 1 / 7  E) 1 / 24

Rationale: "let x be the number of upgraded sensors on the satellite . the number of non - upgraded sensors per unit is x / 6 . the number of non - upgraded sensors on the whole satellite is 24 ( x / 6 ) = 4 x . the fraction of sensors which have been upgraded is x / ( x + 4 x ) = x / 5 x = 1 / 5 the answer is b ."
Answer: B