Answer:
b = 30 km is the answer
Step-by-step explanation:
a = 72 km
b = ?
c = 78 km
According to the Pythagoras theorem,
a² + b² = c²
72² + b² = 78²
5184 + b² = 6084
b² = 6084 - 5184
b² = 900
b = 30 km
∴ b = 30 km is the length of the missing leg
