Answer:
50 mi
Step-by-step explanation:
Two hours after leaving port,
The triangle formed by their tracks and the line joining their current positions is a right-angled triangle.
According to Pythagoras,
a² + b² = c²
30² + 40² = c²
900 + 1600 = c²
2500 = c²
√(2500) = c
c = 50 mi
The boats will be separated by 50 mi two hours after leaving port.