Final answer:
Tiffany can make 1/2 batch of soap bubble mixture with the amount of glycerin she has left.
Step-by-step explanation:
To find the number of batches Tiffany can make, we need to divide the amount of glycerin she has left by the amount she needs for each batch. She needs 1 1/2 cup of glycerin for each batch, and she has 3/4 cup left. So, the number of batches she can make is: 3/4 ÷ 1 1/2 = 3/4 × 2/3 = 6/12 = 1/2 batch.