To find out how much cheese Rosa has left, we first need to determine how much cheese she initially bought and then subtract the amount she used for macaroni and cheese.
Rosa initially bought \( \frac{9}{4} \) pounds of cheese. She used \( \frac{3}{2} \) pounds of that cheese.
We need to subtract \( \frac{3}{2} \) from \( \frac{9}{4} \). To do this, we need a common denominator. The least common denominator of 2 and 4 is 4.
Now we convert \( \frac{3}{2} \) to have a denominator of 4:
\[ \frac{3}{2} = \frac{3 \times 2}{2 \times 2} = \frac{6}{4} \]
Now we can perform the subtraction:
\[ \frac{9}{4} - \frac{6}{4} = \frac{9 - 6}{4} = \frac{3}{4} \]
So, the amount of cheese Rosa has left is \( \frac{3}{4} \) pounds.