Logan is a land surveyor. He wants to determine d, the distance across a lake that cannot be directly measured. He draws this diagram to help him.

A right triangle with side length 7 kilometers, d, and hypotenuse of 9 kilometers.

What is the approximate distance across the lake, to the nearest tenth of a kilometer?
5.7 km
6.3 km
11.4 km
16.0 km