I need help on this badly please come with good explanation on how to slove problems like this.

Step-by-step explanation:

This is a parabola. Because of that, the extreme exists at either the highest point on the graph or at the lowest point on the graph (which is also known as the vertex). This is a positive parabola, so the vertex is a minimum. The coordinates of the vertex are (4, -2.5). The 4 is the x value; therefore, the value of x where the polynomial has an extreme (or extrema) is at x = 4