Given the equation:
y = 828000 - 2700x
Where y is the value of the building and x is the number of months of use.
Let's find when the value of the building will be $666,000.
To find when the value will be $666,000, substitute 666000 for y in the equation and solve for x.
y = 828000 - 2700x
666000 = 828000 - 2700x
Subtract 828000 from both sides:
666000 - 828000 = 828000 - 828000 - 2700x
-162000 = -2700x
Divide both sided by -2700:

The value of the building will be $666,000 after 60 months.
Now, let's convert from months to years.
Where:
12 months = 1 year

Therefore, the value of the building will be $666,000 after 5 years.
ANSWER:
5 years.