Please help ASAP thank you

2.30+0.4-0.88+1.33 can u explain the answer to this why the answer is 3.15

There were 816 people at a concert when a band started to play. after each song, only half the people stayed to hear the next song. how many people were left at the concert after x songs? write a function to represent this scenario.

Will give brainliest what is the value of x? enter your answer in the box.