84.9mm (option D)
Step-by-step explanation:
For a square, all sides are equal
The formula for the diagonal:

Since the sides are equal, the length a
nd the width will be the same
length = 60mm
width = 60mm

![\begin{gathered} \text{square root both sides} \\ \sqrt[]{\text{diagonal}^2}\text{ = }\sqrt[]{7200} \\ \text{diagonal = }84.85 \end{gathered}](https://img.qammunity.org/2023/formulas/mathematics/college/xng09s8h2hw0x6z1kf2pke11up5oo7pvb8.png)
To the nearest tenth, the measure of the diagonal of the square is 84.9mm (option D)