Afish tank, in a shape of rectangular prism, measures
100 cm × 60 cm × 40 cm. the water level reached the
midpoint of the base (the 50 cm mark), when the tank
was tilted to rest on a 60 cm edge, as shown in the
diagram on the right. what would be the depth of the
water, if the tank is returned to its horizontal position
(resting on its 60 cm × 100 cm base)?

The deep of the water would be 20 cm

Step-by-step explanation:

step 1

Find the volume of the water

The volume of the water is equal to

we have

substitute

step 2

Find the deep of the water, if the tank is returned to its horizontal position

(resting on its 60 cm × 100 cm base)

Now we have

substitute the given values

solve for H

therefore

The deep of the water would be 20 cm

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.