Let the total distance to be calculated be s and the soldier's speed be x, then each group is 1/4s, 1.5x, 3/4s, 15/ 16x respectively, and list the equations: soldier t = s/x.

Group t=( 1/4s divided by 1.5x)+(3/4s divided by 15/ 16x) gives (29/30)s/x=29/30T.

So this group of people arrived first.