Mischa dives from a platform that is 10 meters above water. Her dive takes her 3.8meters below the surface of the water. How far does Mischas dive take her

The distance from (10 meters above) to (3.8 meters below) is

(10 + 3.8) = 13.8 meters

Mischa's dive takes her 13.8 meters. First she starts from 10 meters above water, then she goes down to 3.8 meters below the water.

She gets down to sea level, at zero, and that's 10. And then she goes even farther down. 3.8 meters farther down. So you just add 10 and 3.8 to get 13.8 meters.