Because anything multiplied by one is that number. If you have 3/4 one time, then it is 3/4.
You have the following function:

Derivate implictly the previous expression, as follow:

Where you have used that:

Then, the implicit derivative of the given expression is:

Next, solve for y' as follow:

Answer:
EK = 9
Step-by-step explanation:
x + 11 = -5 + 2x -5 + 2x
x+11 = -10 + 4x
11 = 3x - 10
3x = 21
x = 7
EK =-5 + 2 × 7
EK = 14 - 5
EK = 9