The binary string $01000110001000$ is a floating$-$point number expressed using the $14-$bit simple model $(1$ sign bit, $5$ exponent bits using excess$-15$ representation, and $8$ significand bits with no implied bit$).$ What is its decimal equivalent?

$0\mathrm{.}25$

$2\mathrm{.}125$

$1\mathrm{.}25$

$0\mathrm{.}125$