Six consecutive numbers add up to a total of 45. What is the highest of these numbers?

let the numbers be

x, x+1, x+2, x+3, x+4, x+5

adding them:
6x + 15 = 45

6x = 30
x = 5
the largest is x+5 = .......

or, consider if they were all the same: 45/6 = 15/2 = 7.5

Now you know that there are 3 above and three below this, so they are
5,6,7,8,9,10