The difference of the helicopter and the submarine being 18.5 meters makes 18.5+-7.75=10.75
39 it's an arithmetic sequence in which the common difference is +7
P=2(L+W)
if length=7
and P=24
24=2(7+W)
divide both sdes by 2
12=7+W
minus 7both sides
5=W
width=5meters
