You are standing 050 m in front of a lens that projects an i

You are standing 0.50 m in front of a lens that projects an image of you onto a wall 1.9 m on the other side of the lens

Part A

What is the focal length of the lens?

Express your answer in meters to two significant figures

Part B

What is the magnification?

Express your answer to two significant figures.

A) 1/d_o + 1/d_i = 1/f

=> 1/0.50 + 1/1.9 = 1/f

=> f = 1.9 * 0.50 / (1.9 + 0.50) = 0.40 m

B) m = -d_i / d_o = -1.9 / 0.50 = -3.8