$Q _ { d } = 100 - 5 P + 0.004 M - 5 P _ { R }$

$Q _ { d } = 100 - 5 P + 0.004 M - 5 P _ { R }$ ,where P is the price of good X, M is income, and $P _ { R }$ is the price of a related good, R.
-Income is $80,000, and the price of the related good is $40. Also let consumers' tastes change so that consumers now demand 100 more units at each price. When the price of the good is $50, how many units of the good are demanded?

A) 70
B) 200
C) 220
D) 100
E) none of the above