A satellite is composed of 30 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 correct choice from the following answers:
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 30 ( x / 6 ) = 5 x . the fraction of sensors which have been upgraded is x / ( x + 5 x ) = x / 6 x = 1 / 6 the answer is c ."
Answer: C