If you look closely at the graph, if has two lines
One is decreasing and the other one is increasing
The decreasing graph is the one on the left sloping downwards and the increasing one is the one on the right sloping upwards
A graph decreases when as the value of x increases, the value of y decreases
From the graph, the decreasing part starts from the negative x-axis on the left which corresponds to minus infinity and ends at x = 3.
Therefore, the interval of the graph is decreasing at
[tex](-\infty,3\rbrack[/tex]
