To find the total cost if Winonna and Takoda buy their mother the set of power tools, you would typically calculate the cost of the item plus any applicable sales tax. However, since you mentioned that there is no sales tax in the state where they live, the expression would simply be the cost of the power tools itself represented as \( d \).
In the options provided:
- \( d + (d \times 0.15) \) would represent the cost plus 15% sales tax.
- The expressions with other combinations involving addition and subtraction with \( 0.15 \) or \( d \) appear to imply a tax or discounts, but since there's no tax, they would not capture the intended situation correctly.
Given that there is no sales tax, the total amount Winonna and Takoda would pay for the power tools is simply:
\[ d \]
Thus, none of the provided responses accurately represent the cost based on the information given that there is no sales tax. If the task is to use the correct term, only \( d \) accurately represents the cost without additional modifiers like tax.