This problem will give you a taste of how we model gravitational lens systems to measure galaxy masses. Imagine you observe a galaxy lens system with distances Dl = 940 Mpc, Dls = 1,293 Mpc, and Ds = 1,745 Mpc. One image appears at an angular position of θ+ = 1.05" from the lens galaxy, while the other appears at an angular position θ- = -0.35" on the opposite side of the galaxy. You may assume the lens is circularly symmetric.

assume the galaxy can be modeled as an isothermal sphere. Again find the Einstein radius and the mass enclosed by the Einstein radius