The new height of the water is = 9.34 inches (approx)
Step-by-step explanation:
Given, a rectangular container measuring 20 inches long by 16 inches wide by 12 inches tall is filled to its brim with water.
Let the new height of water level be x inches.
The volume of the container = (20×16×12) cubic inches
=3840 cubic inches
According to the problem,
3840 - (20×16×x) = 850
⇔3840 -320x = 850
⇔-320x =850-3840
⇔-320 x = -2990

⇔x = 9.34 inches
The new height of the water is = 9.34 inches (approx)
If two fractions have the same denominators, then just simply add up the numerators together and keep the denominator.
Examples:

FASLE!!! because -23+611=588