Answer:
b = 56km is the answer.
Explanation:
a (Northbound train) = 33km
b (Eastbound train) = ?
c (Distance between them) = 65km
According to the Pythagorean theorem,
a² + b² = c²
33² + b² = 65²
1089 + b² = 4225
b² = 4225 - 1089
b² = 3136
b = 56km
∴ the eastbound train has travelled 56km.