Given and .find
a)
this is my step:
I do not think your answer is correct. I imagine you're supposed to use the properties of logarithms to combine the given information in such a way that you can compute the required logarithm. Note that the bases are different. What do you suppose you have to do there?
Hang on. Just saw something in the OP. Try re-computing the last number from the second-to-last line. That's an average. Your answer at the end is clearly wrong, but I think the steps up to that point are correct.
[EDIT] Earboth sees the problem correctly.