A thin lens with two concave surfaces one with a radius of

Question

Solve the given problem:

Problem: A thin lens with two concave surfaces, one with a radius of curvature magnitude of 20 cm and the other with a radius of curvature magnitude of 30cm am gas an index of refraction of 1.5.

Part A: What us the focal length of the lens?

Part B: If an object is 50 cm from the lens, what is the lateral magnification?

Show me the each step of above problem.