Westbound boats speed = X
Southbound boats speed = X + 5
In 3 hours they are 27 miles apart:
3X + 3(x+5) = 27
Simplify:
3x + 3x +15 = 27
Combine like terms:
6x + 15 = 27
Subtract 15 from both sides:
6x = 12
Divide both sides by 6:
x = 12/6
x = 2
Westbound was 2 miles per hour
Southbound was 2 +5 = 7 miles per hour
Check:
2 miles per hour x 3 hours = 6 miles
7 miles per hour x 3 hours = 21 miles
21 + 6 = 27 miles