Answer: 2.58
Step-by-step explanation:
Portfolio beta of 1.60 is weighted average of all the constituent betas.
US Treasury bills are riskless so beta is 0
Stock A has market risk so beta is 1.
1.60 = (0.16 * 0) + ( 0.36 * 1) + ( 0.48 * b)
1.60 = 0.36 + 0.48b
0.48b = 1.24
b = 2.58