Question 1142545
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As posted, the problem makes no sense.<br>
(1) The questions that are asked concern only sequence X, so the given information about sequence Y is irrelevant.<br>
(2) Then, given only sequence X with first term 4a and sixth term 256, there is not enough information to determine a single solution.  There are an infinite number of geometric sequences with first term 4a and sixth term 256.<br>
Either the problem is flawed, or you have left out some required information in your presentation of the problem.