Infinite geometric sequences and series

Geometric term and sum-to-infinity parameter

[Maximum mark: 6]Consider the infinite geometric sequence. $3,3x,3x^2,3x^3,\ldots$(a) Write down the $12^{th}$ term of the sequence in terms of $x$.[3](b) Given that the sum to infinity of the sequence is $\frac73$ Find the value of $x$.[3]