1/2. Because 3 cancel 3 and 2 can go in 4 twice.
2=1.04^t
t=ln2/(ln1.04)
t=17.673 (approx)
so t=18 (although you will have slightly more than double)
Volume is length time width time height
V = l x w x h
V = 3 x 12.5 x 8.4
V = 315 <<<This is the volume
Hope this helped!