How Fast is C Moving Relative to B?

[Dr. Science]

Homework Statement

relative to A, B is moving towards A at a speed of 0.4c. Farther out C is moving towards A at a speed of 0.5c. all motion is along the x-axis

how fast is C moving relative to B?

Homework Equations

U = (U' + V) / 1+ VU'/c^2

The Attempt at a Solution

0.4c- 0.5c / 1 - (0.4c * 0.5c) / c^2 = 0.125


C is moving at c/8 towards B

?

 

[Spinnor]

As the problem is stated I'm not sure if B and C are heading in the same direction or heading towards each other. All we know for sure is that both B and C are moving towards A.