Data Sufficiency

Q. In a certain company the no. of shares is directly proportional to its face value v, which in turn is indirectly proportional to its book value b. If n=40, then what is the value of V?

I. V =11 wherever b= 9

II. b= 10 wherever n=20


a. Statement (I) ALONE is sufficient, but statement (II) alone is not sufficient.
b. Statement (II) ALONE is sufficient, but statement (I) alone is not sufficient.
c. BOTH statements TOGETHER are sufficient, but NEITHER statement ALONE is sufficient.
d. Each statement alone is sufficient.
e. Statement (I) and (II) TOGETHER are NOT sufficient to answer the question asked, and additional data are needed.

someone please explain..

n = kv (v is face value, n is no. of shares and k is constant)
v=m/b (m is another constant)
n=40
v=40/k
a) m=9*11=99
this helps in finding m and not k. insufficient
b)n=km/b -> km=400
insufficient

a&b) k=400/99
thus v=40/(400/99) = 9.9
Sufficient
IMO C

cans wrote:n = kv (v is face value, n is no. of shares and k is constant)
v=m/b (m is another constant)
n=40
v=40/k
a) m=9*11=99
this helps in finding m and not k. insufficient
b)n=km/b -> km=400
insufficient

a&b) k=400/99
thus v=40/(400/99) = 9.9
Sufficient
IMO C

Even my approach was the same..but OA is A

Hi GMAT Experts,

Can someone shed more light on this please? Is should be "C", but official answer is "A".

Thanks.