Which one of the following tables is a relation that represents a function?

Table 3

Explanation:
For a relation to be a function, each x value should have only one corresponding y value.

Now, let's check the givens: 
Table 1:
x = 1 has two corresponding y-values. Therefore, this is not a function

Table 2:
x = 10 has two corresponding y-values. Therefore, this is not a function.

Table 3:
each x value has only one corresponding y-value. Therefore, this one is a function

Table 4:
x = 7 has two corresponding y-values. Therefore, this is not a function.

Hope this helps :)