No. To test whether a graph is a function or not you do the vertical line test where if a vertical line touches more than one point it is not a function
8/20 is greater than 2/10. If you were to make the denominators the same, by mulipling 2x2 and 10x2, you would get 4/20, which is less than 8/20.
The expression shown is an arithmetic expression. An arithmetic expression results in a numeric value.
The answer by the way is -6.