F(x)=125-(125*0.2x)
to find the value of the phone after 3 years, you put x=3.
f(3)=125-(125*0.2(3))
f(3)=50
The 4 litres of red has to be 2 parts of the mixture, so each part will be 2 litres. Therefore 3 parts of cream will be 6 litres and the one part of blue will be 2 litres.
Answer:
Average rate of change=-3
Step-by-step explanation:
The average rate of change is given by the relation between the values of f(x) and x, in two different points as follows:

In this case, 
Therefore,

.35x+45=y
x is the miles they run
.35 shows that they charge 35 cents per mile
45 is the constant or the fee they always charge to use their vehicle