Domain, range, and is it a function?

What is this inequality notation? t is less then or equal to 2

The graph represents the gallons of water in a water tank with respect to the number of hours since it was completely filled

The fence around a quadrilateral-shaped pasture is 3a^2+15a+9 long. three sides of the fence have the following lengths: 5a, 10a-2, a^2-7. what is the length of the fourth side of the fence?