GMAT Problem Solving (PS) | During a two-year period, the water level in a lake decreased by 20 pe

During a two-year period, the water level in a lake decreased by 20 percent by the end of the first year and increased by 10 percent by the end of the second year. If the lake began the period with a water level of w feet, what was the level, in feet, by the end of the period?

A. 1.2w
B. 1.1w
C. 0.9w
D. 0.88w
E. 0.8w