Answer:
The third graph is correct
Explanation:
Hiiii,
Since the sign is < and doesn't have a line underneath (or equal to), it means we have an open circle. We also know that the line has to go to the left because all the values that go to the left make the inequality true. If they go to the right, it won't be true because the value will be greater than 21 and we need it to be less than 21.
Hope this helps :)