What is the best description of the relation?

Answer:
The relation is not a function.
Step-by-step explanation:
A function is a relation in which no two ordered pairs have the same input and different outputs. Whenever you're trying to determine whether a given relation is a function, observe whether each input corresponds with exactly one output.
In this case, the answer is no. The input value of 10 corresponds with two output values, 4 and 20. It only takes one input value to associate with more than one output value to be invalid as a function.
Therefore, the given relation is not a function.