Question

The water level in a lake was 22 inches below normal at the beginning of March. The water level decreased by 3 1/6 inches in March and increased by 1 6/7 inches in April

Answer 1

At the beginning it was 22 inches below normal (-22).
Then it decreased by 3 1/6 (-19/6).
Then increased by 1 6/7 (+13/7)

-22 - 19/6 + 13/7
-924/42 - 133/42 + 78/42
-1057/42 + 78/42
-979/42
-23 13/42

It was 23 13/42 inches below normal after April.