Use the passive sign convention and determine the amount of power in the element represented by the white box for the follow cases.

$a.$ $V_1 = 6 V$ and $I = 3 A$
$P =$ $W$

$b.$ $V_1 = 6 V$ and $I = -1.5 A$
$P =$ $W$

$c.$ $V_1 = -12 V$ and $I = 3 A$
$P =$ $W$

$d.$ $V_1 = -12 V$ and $I = -1.5 A$
$P =$ $W$