Help with Traveling Wave problem please

A spherical wave with a wavelength of 2.0 m is emitted from the origin. At one instant of time, the phase at r = 4.0 m is pi rad. At that instant, what is the phase at r = 3.5 m and r = 4.5 m?
Answer in rad.

We have to assume the "origin" referred to is the distance coordinate rather than time.

So 0.5m either side of r = 4m represents 0.5 / 2 = 0.25 wavelengths = pi/2 radians of phase

So:
at r = 3.5 m the phase is pi - pi/2 = pi/2 radians
at r = 4.5 m the phase is pi + pi/2 = 3*pi/2 radians
(or possibly vice versa!)