Y is the independent variables
k is the dependent variable
H is 3 . I used the formula for a cone
Let
x--------> the speed of the girl in step
y--------> the speed of the escalator in step
d------> the distance between ground and floor.
we know that

when the girl is going up on escalator
----> equation 
when the girl is going down on escalator
-------> equation 
Adds equation
and equation 

--------> equation 
Time to climb (in step) with y=0 (escalator standing still)
-----> equation 
Substitute equation
in equation 

therefore
the answer is

1. 1750 each week, 2000-1750=250... 250×7=1750.
2. 30 apples. 5×2=10.. 15×2=30
3.Ronald by 9 inches.. 4 feet 6 inches-3feet 9 inches= 9 inches.