$1, 15, 16, 31, 47, 78, 125, ?$

In each of the following questions a number series is given. After the series a number is given followed by $(a),$ $(b),$ $(c),$ $(d),$ and $(e).$ You have to complete the series starting with the number given,following the sequence of the original series and answer the questions that follow the series.

$85$	$43$	$44$	$67.5$	$137$	$345$
$125$	$(a)$	$(b)$	$(c)$	$(d)$	$(e)$

What will come in place of $(c)?$

Find the missing term in the series: $17, 9, ?, 16.5, 35, 90$.

$1015, 508, 255, 129, 66.5, ?$

$2, 8, 16, 128, ?$

$13, 25, 61, 121, 205, (?)$