A particular distant star is found to be 92c . y from Earth. On a direct line

Question:

A particular distant star is found to be 92c . y from Earth. On a direct line between us and the star and 35c . y from the distant star is a dense white dwarf star with a mass equal to 3 times the Sun’s mass M_Θand a radius of 104 km. Deflection of the light beam from the distant star by the white dwarf causes us to see it as a pair of circular arcs like those shown in Figure 2-22(b). Find the angle 2α formed by the lines of sight to the two arcs.

Figure 2-22 (b) Gravitational lens has the same effects on the light from Viewer distant galaxies seen at Earth.