How can instantaneous velocity be found by the graphical method?

(N/A) To find the instantaneous velocity at a specific time $t$ from an $x-t$ (position-time) graph:
$1$. Identify the point $P$ on the curve corresponding to the time $t$ at which the instantaneous velocity is required.
$2$. Draw a tangent to the curve at point $P$.
$3$. The slope of this tangent line gives the instantaneous velocity at that time $t$.
$4$. Mathematically,the slope is calculated as $v = \frac{dx}{dt} = \lim_{\Delta t \to 0} \frac{\Delta x}{\Delta t}$.
$5$. As shown in the graph,by taking smaller and smaller time intervals $\Delta t$ around $t=4 \ s$,the secant lines (like $P_1P_2$,$Q_1Q_2$,$T_1T_2$) approach the tangent at $P$,and their slopes approach the value of the instantaneous velocity at $t=4 \ s$.