Explain question no 15 breifly under 30 mins

Dear Student,

Old Share of X,Y and Z = 4:2:1
Z retires. His share will be taken by X and Y equally.
New Profit Share of X = 4/1 + 1/2 = 9/2
New Profit share of Y = 2/1 + 1/2 = 5/2
Therefore, the ratio amongst X and Y will be 9:5.

Regards