Because:

3 gardens +2 triangles =54

2 gardens +3 triangles =56

So:

5 gardens +5 triangles =56 +54= 1 10.

Draw:

1 Garden+1 Triangle = 1 10÷5=22.

Therefore:

2 gardens +2 triangles =22×2=44

1 Garden =54-44= 10

1 triangle =22- 10= 12