Answer:
A isn't a function due to there being multiple y values for a singular x value in many cases, and B is a function due to having a singular y value per x value
Explanation:
In algebra there is a test for finding out if something is a function called the "vertical line test". If at any point on a graph, a vertical line (straight up and down) is shown to intersect the curve at multiple points, it's not a function. This is because a function must have just ONE y value for every x value, this is a hard and fast rule in this level of math. When your vertical line hits at more than one point, this rule is violated. On graph A, take x = 0. You clearly see that there are 2 y values, -7 and 17, for just that one x value. Graph A isn't a function.
B is a function since in the table there's only one value of y for each value of x. That's it; it matches the rule. Hypothetically, if it had, say, x = 9, and then y = 19 AND 20, that would be two values of y for one value of x and wouldn't be a function.