Answer:
Here is the C++ program:
#include <iostream> //to use input output functions
using namespace std; //to identify objects cin cout
 
int main(){ //start of main method
 
 double risingLevel; //declares a double type variable to hold rising level
 cin>>risingLevel; //reads the value of risingLevel from user
 
 cout<<"Level: "<<risingLevel<<endl; //displays the rising level
 cout << "Years: 5, Rise: " << risingLevel * 5<<endl; //displays the rise in ocean level over 5 years
 cout << "Years: 10, Rise: " << risingLevel * 10<<endl; //displays the rise in ocean level over 10 years
 cout << "Years: 50, Rise: " << risingLevel * 50<<endl; //displays the rise in ocean level over 50 years
}
Step-by-step explanation:
The program works as follows: 
Lets say the user enters rising level 2.1 then,
risingLevel = 2.1
Now the first print (cout) statement :
cout<<"Level: "<<risingLevel<<endl; prints the value of risingLevel on output screen. So this statement displays:
Level: 2.1 
Next, the program control moves to the statement:
 cout << "Years: 5, Rise: " << risingLevel * 5<<endl; 
which computes the rise in ocean levels over 5 years by formula:
risingLevel * 5 = 2.1 * 5 = 10.5
 It then displays the computed value on output screen. So this statement displays:
Years: 5, Rise: 10.5 Next, the program control moves to the statement:
 cout << "Years: 10, Rise: " << risingLevel * 10<<endl; 
which computes the rise in ocean levels over 10 years by formula:
risingLevel * 10 = 2.1 * 10 = 21
 It then displays the computed value on output screen. So this statement displays:
Years: 10, Rise: 21 
Next, the program control moves to the statement:
 cout << "Years: 50, Rise: " << risingLevel * 50<<endl; 
which computes the rise in ocean levels over 50 years by formula:
risingLevel * 50 = 2.1 * 50 = 105
 It then displays the computed value on output screen. So this statement displays:
Years: 50, Rise: 105 Hence the output of the entire program is:
Level: 2.1 Years: 5, Rise: 10.5 Years: 10, Rise: 21 Years: 50, Rise: 105 
The screenshot of the program and its output is attached.