If x, 5.4, 5, 9 are in proportion, then x is equal to:

1. 3

2. 9.72

3. 25

4. $\dfrac{25}{3}$

The fourth proportional to 5, 8, 15 is :

1. 18

2. 20

3. 21

4. 24

The third proportional to 38 and 15 is :

1. $\dfrac{15}{38 \times 38}$

2. $\dfrac{38 \times 38}{15}$

3. $\dfrac{15 \times 15}{38}$

4. $\dfrac{38 \times 15}{2}$

The third proportional to (x² − y²) and (x − y) is :

1. $\dfrac{x - y}{x + y}$

2. $\dfrac{x + y}{x - y}$

3. (x + y)

4. (x − y)