Answer:
[tex]\dfrac{d-6}{2}[/tex]
Explanation:
Diana's age is d.
Carol is 3 years younger than half of her sister Diana's age.
Carol's age = [tex]\dfrac{d}{2}-3[/tex]
Where d is Diana's age.
[tex]C's\ age =\dfrac{d-6}{2}[/tex]
Hence, Carol's age is [tex]\dfrac{d-6}{2}[/tex].