Answer:
To determine the answer to the proper number of significant figures, we need to consider the significant figures in the given numbers and apply the rules of significant figures during addition -
15.22 (2 significant figures) + 75 (2 significant figures) = 90.22 (4 significant figures)
15.670 (5 significant figures) + 90.22 (4 significant figures) = 105.890 (5 significant figures)
28.1 (3 significant figures) + 105.890 (5 significant figures) = 134.990 (5 significant figures)
28.120 (5 significant figures) + 134.990 (5 significant figures) = 163.110 (6 significant figures)
To state the answer to the proper number of significant figures, we should round it to the appropriate number of significant figures based on the least precise number involved in the calculation, which is 28.12 (4 significant figures). Therefore, the final answer is 163.1.