In Fruit Flies,the Recessive Pr and Cn Mutations Cause Brown

In fruit flies,the recessive pr and cn mutations cause brown and bright-red eyes,respectively (wild-type flies have brick-red eyes) .The double mutant pr cn combination has orange eyes.A female who has wild-type eyes is crossed to an orange-eyed male.Their progeny have the following distribution of eye colours: $$\begin{array} { | l | r | } \hline \text { wild-type } & 8 \\\hline \text { brown } & 241 \\\hline \text { bright-red } & 239 \\\hline \text { orange } & 12 \\\hline & 500 \\\hline\end{array}$$
What is the map distance between the pr and cn genes?

A) 20 m.u.
B) 2 m.u.
C) 4 m.u.
D) 46 m.u.
E) 8 m.u.