Answer:

Explanation:
Let
x ---> the number of an adult tickets
y ---> the number of a child tickets
Remember that the word "at least" means "greater than or equal to"
so
The number of an adult tickets multiplied by its price ($18) plus the number of a child tickets multiplied by its price ($12) must be greater than or equal to $300
The inequality that represent this situation is

using a graphing tool
the solution is the shaded area
Remember that the number of tickets cannot be a negative number
see the attached figure