There are four train routes between A and B, and three train routes between B and C. Find the number of ways that a person can travel by train: i. from A to C by way of B; ii. roundtrip from A to C by way of B; iii. roundtrip from A to C by way of B without using a train lines more than once.

1) By using Fundamental Principle of Counting ,the number of way that a person can travel by train from A to C by way of B $=4×3=12$ .

2) The number of way that a person can travel by train from A to C by way of B $=4×3=12$

Therefore , roundtrip from A to C by way of B$=12×12=144$

3)Round trip from A to C by way of B without using a train line more than once $=12×6=72$