To find the sale price of an item that costs \( d \) dollars with a 30% discount, you would calculate 30% of \( d \) and then subtract that amount from the original price.
- Calculate the discount: 30% of \( d \) is \( 0.3d \).
- Subtract the discount from the original price: The sale price would be \( d - 0.3d \).
This simplifies to:
\[ d - 0.3d = 0.7d \]
Thus, the correct expression to find the sale price is 0.7d.
So the answer is 0.7 d.