The observatory in the John Hancock Center in Chicago is located in the top floor, 900 feet above the ground. The express elevator travels nonstop from the ground floor to the observatory on the top floor at a rate represented by the equation y=30x, where y is the height, in feet, and x is the number of seconds.

Step-by-step explanation:

Given the rate at which the elevator travels modeled by the expression;

y = 30x where y is the height, in feet, and x is the number of seconds.

If the observatory in the John Hancock Center in Chicago is located in the top floor, 900 feet above the ground, we can calculate the time taken to reach the top floor by substituting y = 900 into the equation and solve for x as shown;

y = 30x

900 = 30x

Rearrange

30x = 900

Divide both sides by 30

30x/30 = 900/30

x = 30

Hence it takes 30seconds for the elevator to reach the top floor