Answer:
f(x) = 4 - x
Step-by-step explanation:
'f(x) = blah-blah' is the same as saying 'y = blah-blah', except it is also telling you that the x-y relationship is a function.
I notice that for each case, x + y = 4, so y = 4 - x
Or in 'function' terminology, f(x) = 4 - x
Answer:

Step-by-step explanation:
Given: 
To find: average rate of change of the function
over the interval
and 
Solution:
Take 
Find 

Average rate of change of the function 

Base of the courtyard = sqrt(90) = 3sqrt(10)
Height of the courtyard = 10 + sqrt(3)
Area of the courtyard = 1/2 x 3sqrt(10) x (10 + sqrt(3)) = 15sqrt(10) + 3/2sqrt(30)