Numerical aptitude - Equilibrium

You have to discover the value of the unknown weight that will keep the scales balanced.
The turning force on one side must equal the turning force on the other.
Weights turning force are equal to weight value per distance from pivot. The real force of a weight is equal to its value multiplied by its position.

Level 1

[1] Weights 19 and 22 - [2] Weights 19 and 10 - [3] Weights 12 and 2 - [4] Weights 32 and 50 - [5] Weights 20 and 30 - [6] Weights 17 and 25 - [7] Weights 14 and 6 - [8] Weights 24 and 27 -

Level 2

[9] Weights 11 and 9 - [10] Weights 10 and 8 - [11] Weights 13 and 7 - [12] Weights 2+8 and 4 - [13] Weights 5 and 1+6 - [14] Weights 7 and 9 -

Level 3

[15] Equilibrium with 6+2 - [16] Weights 10+6 and 6 -