Answer: The third grid
Explanation:
0.3 x 3 is equal to 0.9.
0.9 can also be interpreted as 9/10.
The grids all have 10 columns.
So you are looking for the grid with 9 out of 10 columns shaded.
The third grid is the only grid with 9/10 columns shaded.
So the answer is the third grid.