The Observed Solubility of the Salt MX in 4

The observed solubility of the salt MX in 4.0 M strong acid is 2.30 × 10^-3 M. The K_a value for the acid HX is 1.00 × 10^-9. Calculate the value of K_sp for the salt MX.

A) 1.3 × 10³
B) 1.3 × 10^-15
C) 5.3 × 10^-6
D) 1.3 × 10^-6
E) 5.3 × 10^-15