Answer
At the given point of the graph the instantaneous rate of change, the slope of the tangent and the value of the derivative are equal to each other.
Work Step by Step
The instantaneous rate of change at $a$ is
$$\lim_{x\to a}\frac{f(x)-f(a)}{x-a}.$$
The slope of the tangent at the given point $(a,f(a))$ is
$$m_{tan}=\lim_{x\to a}\frac{f(x)-f(a)}{x-a}.$$
The value of the derivative of the function $f$ at the point $a$ is given by deffinition as
$$f'(a)=\lim_{x\to a}\frac{f(x)-f(a)}{x-a}.$$
We see that at the given point of the graph the instantaneous rate of change, the slope of the tangent and the value of the derivative are equal to each other.