You are given the following partial demand and forecast data for a product:

$\backslash$table$[[$Quarter $($t$)$:$,4,5,6],[$Forecast $($Ft$)$:$,400,430,600],[$Demand $($Dt$)$:$,420,370,680]]$

Forecast for quarter $7$ was $490.$ The actual demand for quarter $7$ turned out to be $1060.$ Compute a demand forecast for quarter $8$ using exponential smoothing with $a=0\mathrm{.}15.$

A$.F8=575$

B$.F8=490$

C$.F8=974\mathrm{.}5$

D$.F8=1060$