In this company, every year all the workers have to vote to choose the CEO.
Throw a ballot in the ballot box to vote.
This is a jukugo word, which usually means on'yomi readings from the kanji. If you know the readings of your kanji you'll know how to read this as well. You may have to think back to some other words using 投 to remember the on'yomi reading, 投資 for example.