2 problems here:

The first one(#74)does not look as if it has an error, the standard formula being a_{1}r^{(n-1)}to find the n^{th }term.

The second problem (#75)completely eludes me, there are answers in the back of my book for both a & b that are all fractions, yet I cannot solve for any.(ie find a way to prove the sequence is either arithmetic or geometric)

Trying to divide to find r gives me a remainder, solving for x does not do much as sequences don't seem to involve zeros. There must be some other way to solve for x that I am failing to see.