Add the same letter to each of the 4-letter words on the right and rearrange each one's letters into a 5-letter word. Write these five letter words in the cells to the left. The words must be such that the added letter always falls properly in the yellow square on that line.
From Mensa Puzzle Calendar 2017 by Mark Danna and Fraser Simpson, Workman Publishing, New York. Puzzle for February 5.