Answer
1979
Work Step by Step
We set the equations equal to find:
$ -.225x+16.1 = .45x + 21.7$
Now, we use PEMDAS, a method for simplification. This acronym reminds us that we must first address parentheses, and then exponents. Next, we address multiplication and division, going from left to right. Lastly, we simplify addition and subtraction from left to right. This gives the year:
1979