Consider the following data:

$\backslash$table$[[$Time$,t,s,0,4,6,8,10,12,14,16,],[$Position$,x,m,0,0\mathrm{.}7,1\mathrm{.}8,3\mathrm{.}4,5\mathrm{.}1,6\mathrm{.}3,7\mathrm{.}3,8\mathrm{.}0,8\mathrm{.}4]]$

Find the acceleration at $t=4s$ using the second$-$order correct forward finite$-$difference method. $($Round the final answers to three decimal places. Include a minus sign if necessary.$)$