Here it is
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A [attachment id=0 msg=2801] B
Rate forward =k[A]
Rate reverse= k_1
At equilibrium Rates are same and Equilibrium constant is the ratio of the rate constant forward direction with rate constant of backward direction
K= k/k_1
The given equations represents the rate laws of first order kinetics in which rate constant is k of e^-kt
Here we know k and k-1
Take ratio of k and k_1and you will get answer as 5