To find the expected number of shoppers who prefer plastic bags, you can use the given probability and the total number of shoppers.
If the probability of preferring plastic bags is 50%, then you can calculate the expected number of shoppers as follows:
\[ \text{Expected number of plastic bag shoppers} = \text{Total shoppers} \times \text{Probability of preferring plastic bags} \]
Given that there are 150 shoppers:
\[ \text{Expected number of plastic bag shoppers} = 150 \times 0.50 = 75 \]
Thus, you can expect that 75 shoppers will prefer plastic bags.
So the correct answer is 75.