To find the diver's elevation when he is \( \frac{2}{3} \) of the way down to the treasure, we first calculate the depth of that point.
The total depth of the treasure is \( 97.2 \) feet. To find \( \frac{2}{3} \) of that depth, we calculate:
\[ \text{Depth at } \frac{2}{3} = \frac{2}{3} \times 97.2 \]
Calculating that gives:
\[ \frac{2}{3} \times 97.2 = 64.8 \]
This means the diver has descended \( 64.8 \) feet down. Since below the surface is represented as a negative elevation, the diver's elevation when he is \( \frac{2}{3} \) of the way down is:
\[ -64.8 \text{ feet} \]
Thus, the correct response is:
−64.8 ft. (negative 64 point 8 ft.)