A railway train crosses another train which is running in opposite direction with speed of $80 \mathrm{km}/\mathrm{hr}$ in $12$ seconds. To find the speed of the first train, the knowledge of which of the two statements (a) and (b) is/are sufficient?

(a) Length of the first train.

(b) Length of the second train.

A boat takes $3$ hours to go from P to Q downstream and from Q to P upstream. What is the speed of the boat in still water?
To know the answer of this question the knowledge of which of the statements (a) and (b) is/are sufficient?

(a) The speed of the current is $1 \mathrm{km}/\mathrm{hr}$

(b) The distance between P and Q is $4 \mathrm{km}$

A train running at a speed of $120 \mathrm{km}/\mathrm{hr}$ crosses another train running in the opposite direction in $9$ seconds.

To find out the length of the first train, the knowledge of which of the statements (P) and (Q) is/are sufficient?

(P) Speed of the second train

(Q) Length of the second train

Train A crosses another train B running in opposite direction in $9$ seconds. What is the speed of the train A?

To know the answer of this question, the knowledge of which of the following statement is/are sufficient?

(a) Speed of the train B

(b) Length of the train A

(c) Length of the train B