Please step by step guide

A stock from $45 at t = 0 to $55 at t = 1. If you are selling this stock short, and assume broker holds proceeds of sale plus requires 50% margin, what is your return on equity over this time period?

A. 0.2222

B. -0.4444

C. 0.4444

D. -0.2222

A stock moves from $45 at t = 0 to $55 at t = 1. If you buy it on margin (50%), and assume zero interest to borrow money from your broker, what is your return on equity over this time period?

A. 0.2222

B. -0.4444

C. 0.4444

D. -0.2222