The fourth proportional to 0.12, 0.21 and 8 is :

1. 8.9

2. 14

3. 17

4. 56

The mean proportion between 9 and 16 is:

1. 7

2. 12

3. 25

4. 144

The mean proportion between 0.02 and 0.32 is :

1. 0.08

2. 0.16

3. 0.3

4. 0.34