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

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.