Four samples of three observations each have been taken, with actual measurements (in centimeters) shown below. Establish three-sigma mean and range...

For 77 the grand mean is 12.05, not sure where the 11.135 is coming from.For 78 you need to work with percents not numbers. Week 1 is .1, week 2 is .08 and so forth.For 83 the expected number is (60/2)+1=31 with a standard deviation of the square root of (60-1)/4)=3.84. See if you can get the rest.