The figure below shows the position vs$.$ time plot of an object moving in one dimension. The numerical values of the points marked are: $A=-34\mathrm{.}7,B=58,C=14\mathrm{.}4,$ and $D=23\mathrm{.}5$

What is the acceleration at $t=18\mathrm{.}0s(in\frac{m}{s^2})?$

$x(m)$