Help, on 4 problems, please...arithmetic means, summation notation?

[dementia]

I am absolutely terrible at mathematics, and I have a final coming up soon. A few worksheets were handed out on Monday as study guides, and so far these four problems have me puzzled.First problem:Insert three arithmetic means between 4 and 15.Second problem:Find the arithmetic mean between 8 and 19.Third problem:Write the summation notation for the sum.9 + 16 + 25 + 36 + 49 + 64Fourth problem:Write the summation notation for the sum.4 + 8 + 12 + 16 + 20 + 24Any help would be much appreciated. Thanks!

[StephenN]

2nd.13.5