Please answer this correctly

Option 2

Step-by-step explanation:

Last month the change in water level was -13 mm. This month, the water level increase by 13 mm.

-13 + 13 = 0

check the picture below.

well, the angle at the vertex d is clearly not a right-angle, let's check for the one at the vertex f which does look like,   however if it's indeed, that means ef is perpendicular to df, in which case their slopes will be negative reciprocal of each other.

so the negative reciprocal of the slope of ef is 1, however the slope of df is not 1, is 1/2, so nope, they're not perpendicular lines.