The concentration of a certain chemical in a full water tank depends on the depth of the water. At a depth that is x feer below the top of the tank, the concentration is 3+(4/sq rt of 5-x) parts per million, where 0<x<4. To the nearest 0.1 ft, at what depth is the concentration equal to 6 parts per million?
Is substituting the answer choices the best way to solve this?
A) 2.4 ft
B) 2.5 ft
C) 2.8 ft
D) 3.0 ft
E) 3.2 ft
Is this considered a difficult question?
I don't understand the red part of the problem