Answer:
The function f(x) when x=x-4 is
or 
Step-by-step explanation:
Given function f is defined by 
Now to find the function f(x-4):

Put x=x-4 in the above function we get

(using the formula
)

(adding the like terms)


Therefore
or 
The function f(x) when x=x-4 is
or 
Answer:
x=17.5 or 18,y=12.5,or 13
Step-by-step explanation:
20-15 = 5
5÷2 = 2.5
15+2.5 = 17.5
15-2.5=12.5