Logical aptitude - Mathematical operations

Associate each figure with a positive integer and perform the proposed calculations.
To each symbol corresponds the same number, different from those assigned to other symbols or numbers present into equations.

Level 1

[1] Simple fruits - [2] Fruits and starfish - [3] Transportation vehicles - [4] Simple European flags - [5] Simple toys - [6] Other toys - [7] Very simple toys - [8] More toys - [9] Simple Heroes -

Level 2

[10] More fruits - [11] More vehicles - [12] European flags - [13] More European flags - [14] Other European flags - [15] Super Heroes - [16] More Heroes -

Level 3

[17] Hard vehicles -