This is a very easy topic and once you get it, Its just so normal!
When the circle is colored, we use the inequality signs:
Greater than or equal to OR Less than or equal to ≤,≥
And if the circle is not colored, its just
Less than OR Greater than <,>
A first one is not colored, we can deduce that the inequality is: x<18
Why? because the line goes backwards and backwards mean that the number is less.
x is less than 18
B the second one is colored and therefore the inequality is: x≤18
Why? Because x can be 18 or the numbers less than 18.
C x≥18, x can be 18 or greater.
D x<18, x can be any number greater than 18