Hi reiward,

You should have been given the formula for finding the nth term of a geometric sequence.

= common ratio

Your first element ( ) will be 81.

because there are five elements in all between the 5th element and the 9th element, inclusive.

Solve for

Now that you have found the common ratio, substitute back into the original formula and solve for .

This time there are 3 elements from the 3rd to the 5th elements, inclusive. So,

Remember