The simplified expression is
, and the correct answer is: D.

To simplify the expression \(x(2.25 + 1.25 + 0.75)\), distribute the \(x\) to each term inside the parentheses and then combine like terms:
![\[ x(2.25 + 1.25 + 0.75) = x \cdot 2.25 + x \cdot 1.25 + x \cdot 0.75 \]](https://img.qammunity.org/2024/formulas/mathematics/middle-school/oj06o7jlrrb9cy5qzvs1cfmlcf5qno96ns.png)
Combine the coefficients:
![\[ 2.25x + 1.25x + 0.75x \]](https://img.qammunity.org/2024/formulas/mathematics/middle-school/oczl7hdxn9jtmmjzmz7vw49b27x701ybk6.png)
Combine the \(x\)-terms:
![\[ 4.25x \]](https://img.qammunity.org/2024/formulas/mathematics/middle-school/sbpqxdz2qa9zwvdoarhp7ghp2hha5vkkwr.png)
Therefore, the simplified expression is
, and the correct answer is: D.
