least squares homework

I need help with this question and how to proceed
need to rewrite the following regression fitting, can someone assist with this problem. I don't know how to enter subscripts so I indicated sub(): K A e At +K B e Bt , where A and B are given. I need to rewrite K A e^ At +K B e^ Bt in terms of K a , and Ϯb (catcher) , so that K A and Ϯb can be estimated separately? How?

What are the variances of K a after the rewriting and of K b after the second?
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