To calculate the total cost of the apples that Zoe bought, you can multiply the weight of the apples by the price per pound.
Here is the calculation:
\[ \text{Total Cost} = \text{Weight} \times \text{Price per pound} = 1.5 \text{ pounds} \times 3.50 \text{ dollars per pound} \]
\[ \text{Total Cost} = 5.25 \text{ dollars} \]
So, Zoe spent $5.25 on the apples.