**Given information:**
- Rohit reaches the top after taking 40 steps on the moving escalator
- His girlfriend reaches the top after taking 30 steps on the moving escalator
- Rohit's walking speed is one and a half times that of his girlfriend

To find out how many steps Rohit would take to walk up to the top if the escalator is switched off, we first need to calculate the relative speed of Rohit and the escalator.

**Calculating relative speed:**
Let's assume Rohit's walking speed is 'x' steps per unit time and the escalator's speed is 'y' steps per unit time.

Since Rohit's girlfriend takes 30 steps to reach the top, and her walking speed is 'x' steps per unit time, the relative speed for her would be (x - y) steps per unit time.

According to the given information, Rohit's walking speed is one and a half times that of his girlfriend. So, Rohit's walking speed would be (1.5x) steps per unit time.

**Calculating the speed of the escalator:**
To calculate the speed of the escalator, we can subtract the relative speed of Rohit's girlfriend from her walking speed. Therefore, we have:
(x - y) = 30 ----(1)

Since Rohit's walking speed is one and a half times that of his girlfriend, we have:
1.5x = (x - y) ----(2)

Substituting the value of (x - y) from equation (1) into equation (2), we get:
1.5x = 30

Simplifying the equation, we find:
x = 20

**Calculating the number of steps Rohit would take:**
Now that we know Rohit's walking speed, we can calculate the number of steps he would take if the escalator is switched off.

Since Rohit's girlfriend takes 30 steps to reach the top, her relative speed with the escalator is (20 - y) steps per unit time. Using this relative speed, we can calculate the time taken by Rohit's girlfriend to reach the top without the escalator:
30/(20 - y) = time taken by Rohit's girlfriend to reach the top without the escalator

Since Rohit's girlfriend and Rohit both reach the top at the same time, the time taken by Rohit would be the same:
40/(20 - y) = time taken by Rohit to reach the top without the escalator

Since we are looking for the number of steps Rohit would take, we can multiply the time taken by Rohit by his walking speed:
40 * 20/(20 - y) = number of steps Rohit would take

To find the value of 'y', we can substitute the value of 'x' into equation (1):
20 - y = 30 - 20
y = 10

Substituting the value of 'y' into the equation for the number of steps Rohit would take, we get:
40 * 20/(20 - 10) = 40 * 20/10 = 40 * 2 = 80

Therefore, Rohit would take 80 steps to walk up to the top if the escalator is switched off.

Let the walking speed of Rohit be 1.5x and that of his girlfriend be x. Let the speed of the escalator be S steps/unit time, and the number of steps on the escalator be N.