Hydrogen Iodide Decomposes at 800 K Via a Second-Order Process

Hydrogen iodide decomposes at 800 K via a second-order process to produce hydrogen and iodine according to the following chemical equation.
2 HI(g) → H₂(g) + I₂(g)
At 800 K it takes 142 seconds for the initial concentration of HI to decrease from 6.75 × 10^-2 M to 3.50 × 10^-2 M.What is the rate constant for the reaction at this temperature?

A) 5) 12 × 10^-4 M^-1s^-1
B) 9) 69 × 10^-2 M^-1s^-1
C) 10.3 M^-1s^-1
D) 1) 95 × 10³ M^-1s^-1