If the mean of a given data set is 20.6 and the standard deviation is 2.2 ,where will a majority of data lie : a) 18.4 to 22.8 b)20 to 21 c)18.4 to 20.6 if you can tell me how you arrived at your answer. in advance .

The function a represents the cost of manufacturing product a, in hundreds of dollars, and the function b represents the cost of manufacturing product b, in hundreds of dollars. a(t) = 5t + 2 b(t) = 7t - 2t +4 find the expression that describes the total cost of manufacturing both products, a(t) + b(t). a. 7t^2 - 7t + 2 b. 7t^2 + 3 +6 c. 7t^2 + 7t - 6 d. 7t^2 - 3t + 6