Wave B is a P-Wave. I know this, because P-Waves refract when it hits a new substance. Also p-waves travel faster than s-waves, and wave B has a greater velocity.
The mantle starts at about 700 km. I know this, because there is an increase in velocity when the wave reaches about 700 km. The outer core starts at about 2900 km. I know this, because the liquid outer core is new substance, so the s-wave reflected off and the p-wave refracted.
The outer starts at about 2900 km. I know this, because the p-wave refracted and the s-wave reflected off the the liquid outer core.