Chemistry Question? Kinetics?

As the unit of the rate constant M⁻¹•S⁻¹, the reaction is second-order.

Integrated rate equation for second order reaction:
1/[A] = kt + (1/[A]ₒ)
1/[A] = 0.390 × 905 + (1/0.00780) M⁻¹
1/[A] = 481.2 M⁻¹
Concentration after 905 s = 1/481.2 M = 0.00208 M

This is a second order reaction because the units on the rate constant are M^-1 s^-1. The integrated rate law for a 2nd order reaction is:

1/[A] = kt + 1/[A]o
1/[A] = 0.390 M^-1 s^-1 (905 s) + 1/7.80X10^-3 M
1/[A] = 481.16 M^-1
[A] = 2.08X10^-3 M