The answer is 5 because it is consecutive 3 times and it is an odd number
The slope is 3.5, also known as 3 1/2.
Answer:

where
is the number of laptops, and
is the year.
in 2017: 
Step-by-step explanation:
I will define the variable
as the number of years that passed since 2007.
Since the school buys 20 lapts each year, after a number
of years, the school will have
more laptops.
and thus, since the school starts with 31 laptops, the equation to model this situation is

where
is the number of laptops.
since x is the number of years that have passed since 2007, it can be represented like this:

where
can be any year, so the equation to model the situation using the year:

and this way we can find the number of laptos at the end of 2017:

and


X + 0.4[6-x] = 0.5*6 0.6x = 0.6 x = 1 gallon the answer is, "one gallon".