Can somebody explain, how did he get that answers?

by step by step for me to understand easily

Thanks in advance.

b) (4 points) How much of each good does each consumer demand in equilibrium? Consumer A's Demand for X: |2. Consumer A's Demand for Y: 8 Consumer B's demand for X: Consumer B's demand for Y: D (2 points) What is the marginal rate of substitution for consumer A at the competitive equilibrium? Y= 1 MRS = - MVx Initial endowment 3xy My 3 y X