Jennifer,
It helps sometimes to think of a function as a procedure like the square root button on your calculator. You input a number into your calculator, press the square root button to start the procedure working, and you get an output number, or an error message if your input was negative. The domain of the function are the valid inputs (for the square root the domain is all nonnegative numbers) and the range is all possible outputs (for the square root function the range is also all nonnegative numbers).
You have a function (procedure) that is describe by x  2y = 1. The standard notation here is that the letter x stands for the input values and y stands for the output values. You have the range {2, 0, 5, 8} so let's look at 2, that is y = 2. The question is then what input value gives y = 2? In other words what is x if
x  2(2) = 1
x + 4 = 1
x = 3
Now find the x values that produce the other three values in the range.
Penny
