Find $x$, where $x$ is a square number which is divisible by four, and between 39 and 80.
To find a square number that is divisible by four, I need to look for numbers that are squares of even numbers. This is because if I square an odd number, I get an odd number, which is not divisible by four. So I can start by checking the squares of the even numbers between 6 and 10, since those are the only ones that could be between 39 and 80. I can use a calculator or mental math to find that $6^2 = 36$, $8^2 = 64$, and $10^2 = 100$. The only one that fits the criteria is 64, which is a square number, divisible by four, and between 39 and 80. So $x = 64$. 