A crash cushion is to be placed at an elevated expressway gore to safely decelerate a $2040kg$ car traveling at a speed of $88k\frac{m}{h}r.$ Two$-$hundred liter steel barrels with a $178-$mm$-$diameter hole in the center of each end will serve as the basic element. Laboratory studies have indicated that a dynamic force of $40kN$ is required to crush one barrel from its original $0\mathrm{.}6m$ diameter to approximately $0\mathrm{.}15m.$ The dynamic energy consumption is therefore $e_d=0\mathrm{.}45m40kN=18kJ.$ Determine the number and arrangement of barrels that will stop the car and the average deceleration level.