Answer:
211 feet
Step-by-step explanation:
Consider vertical number line, where 0 is at surface of the lake, positive direction - above the lake surface and negative direction - below the surface of the lake.
A rock is thrown into a lake from a bridge 133 feet above the lake's surface, then initial position of the ball was +133.
The rock sinks 78 feet below the lake's surface, then the final rock's position is -78.
Difference: +133 - (-78) = 133 + 78 = 211 feet
