For the reaction 4 NH3(g) + 5 O2(g) \longrightarrow 4 NO(g) + 6 H2O(g), if the rate of change of NH3 (Δ[NH3]/Δt) is -6.0 x 10-3 M/s at a particular time. What is rate of the reaction at the same time?

a. 1.5 x 10-3 M/s
b. -2.4 x 10-2 M/s
c. -1.5 x 10-3 M/s
d. 2.4 x 10-2 M/s