A GPS satellite develops a fault whereby it moves into an orbit $19800$ km above the Earth$$s surface and also emits a weak signal whose power is only $20$ W$.$ What will be the power per square metre of the signal received on the Earth$$s surface? Choose the nearest value from the list below. $($W$/$m$2$ represents $$watts per square metre$.)$

Question $6$Select one:

$4$ x $109$ W$/$m$2$

$4$ x $1017$ W$/$m$2$

$2$ x $1016$ W$/$m$2$

$8$ x $105$ W$/$m$2$

$2$ x $104$ W$/$m$2$

$8$ x $108$ W$/$m$2$

$4$ x $1015$ W$/$m$2$