When you see this equation...

x < 4

What numbers come to mind
that could replace x 
(the one unknown)?

x could be 3, 0, and -5

Could decimals and/ or fractions replace x?

Sure could...  2.4, 1/2, -5/6

Since you know x must be less than 4 we will show the solution set using an arrow pointing to the left of 4.  Since our solution set does not include 4 we will use an open circle on the number 4.

x > -3

The solution set would be all the numbers greater than 3 including the 3.  Why does this solution set include the 3?  The symbol greater than or equal to says so!

We need to show the solution set using an arrow pointing to the right of the 3.  Instead of an open circle we use a closed circle.