# Reaction order of a reaction with catalyst

I am given the following

$$\ce{H2O2 -> H2O + 1/2 O2}$$ (catalysed by $$\ce{KI}$$)

There are two solutions. $$[\ce{H2O2}]$$ is the same in both solutions but $$[\ce{I-}]$$ is $$\pu{0.01M}$$ and $$\pu{0.005M}$$, respectively.

UV absorbance ($$A$$) is measured at $$\pu{240 nm}$$ at different times in a cell with depth $$\pu{0.1 cm}$$. $$\varepsilon_{[\ce{H2O2}]} = \pu{35 M^{-1}cm^{-1}}$$ at $$\pu{240 nm}$$. (Assume that the $$A = 0$$ in a solution without $$\ce{H2O2}$$)

The absorbance over time is:

I am asked to determine the reaction order with respect to $$\ce{H2O2}$$ and $$\ce{I-}$$. I know that in order to determine the reaction order I should have the concentration of the components and plot that against time (in different ways to test all orders) and if the line is linear I have found the reaction order. However, I have never done this with a catalyst nor from absorbance which is why I am having a little trouble with understanding how to solve this.

I assumed that I should use Beer-Lambert's law ($$A=\varepsilon c\ell$$) somehow and from that calculate the concentration of $$\ce{H2O2}$$ but I don't have the absorbance to do so. And for $$\ce{I-}$$, I have the absorbance but not the molar absorbance coefficient to calculate the concentration.

I have tried to find examples or help online but failed to find anything like my problem so I would appreciate if someone could push me in the right direction of solving this problem. Thank you!