Answer
(b) $1.5c $
Work Step by Step
The ether is at absolute rest.
The speed of light with respect to the ether is c.
An observer travelling at speed of 0.5c with respect to the ether is at rest in his reference frame.
If the observer is moving towards the source of light then the light and the observer are moving in opposite directions. So the speed of light with respect to the observer is $0.5c+c=1.5c$
