Find the compound ratio of 2a : 3b, mn : x² and x : n

If (x + 3) : (4x + 1) is the duplicate ratio of 3 : 5, find the value of x.

If (3x - 9) : (5x + 4) is the triplicate ratio of 3 : 4, find the value of x.

If x, 2, 10 and y are in proportion, the values of x and y are respectively :

1. 0.2 and 0.25

2. 0.2 and 50

3. 0.4 and 50

4. 0.4 and 25