What will come in place of the question mark $(?)$ in the following number series?
$3, 9, 27, 81, ?$

What is the value of $S = \frac{1}{1 \times 3 \times 5} + \frac{1}{1 \times 4} + \frac{1}{3 \times 5 \times 7} + \frac{1}{4 \times 7} + \frac{1}{5 \times 7 \times 9} + \frac{1}{7 \times 10} + \dots$ up to $20$ terms?

Find the next term in the series: $17, 9, 15, 40, 143.5, ?$

$325, 314, 288, 247, 191, ?$

$4, 12, 36, 108, ?$

$45, 54, 47, ?, 49, 56, 51, 57, 53$