Answer: Numerical expression for the difference in their heights

The difference in their heights= 7 meters
Explanation:
Given: The height of the Hoover Dam, in the United States = 233 meters
The height of Ertan Dam, in China = 240 meters
let h be the difference in their heights
The difference between the heights of the two dams is given by the numerical expression

Therefore, the difference the heights of the two dams is 7 meters.