Finding First Order Rxn Rate Constant

[BayernBlues]

Homework Statement

I have a first order reaction where I need to find the rate constant. I have the following data:
T = 30'C
the slope of a graph with ln O.D vs T (minutes) is -0.008 so k is 0.008.

The Attempt at a Solution

I'm unsure about what reaction I would need here. This is for an acid sol'n (1 M H2SO4) mixed with a ferrous complex in a spectrophotometer with a 510 nm wavelength. I know there's the formula A = E*l*c where E is epsilon but I don't know how to determine the first order rate constant from this. For first order rate reactions: R = k[A] I know that k is 0.008 but I don't know how to get [A]

 

[Redbelly98]

Isn't the rate constant simply k=0.008/min?