Error in Measurement Sheet. - Upper limits - HELP!!

Ok, I've been dumped with a maths sheet, which I don't have a clue about and I don't even know what it's about. If anyone could give me the answers and help me with the questions you don't know how much I'd appreciate it.

1. The weights of four rowers are 86.3kg, 89.2kg, 85.0 kg and 93.9 kg.

a) Find the upper limit of their total weight

b) Use the answer to a) to find the maximum value of the mean weight

c) Find the minimum value of the mean weight.

2. A room is 3.93 m long and 2.89 m wide correct to the nearest centimetre. Find the lower and upper limits of the area of the room.

There's alot more but could I have help on those for a starter?

Thanks in advance.