Mathematics

Problem

Let

x_1, x_2, x_3, x_4

be in a geometric progression. 2, 7, 9, 5 are subtracted respectively from

x_1, x_2, x_3, x_4

then the resulting numbers are in an arithmetic progression. Then the value of

\frac{1}{24} (x_1 x_2 x_3 x_4)

is: A 18 B 72 C 216 D 36