In the assignment, they wrote:The mean of a set of eight numbers is 3 and the mean of a different set of twelve numbers is x. Given that the mean of the combined set of twenty numbers is 9, calculate x.

My thinking: Since the average of the 8 numbers is 3, and you find this average by dividing the total by 8, then that total is 8*3 = 24, right? So would the total of the others be 12*x, with the combined total being 20*9 = 180? And then you add the two smallers numbers and make this equal to the combined total?