The median is also the number that is halfway into the set. To find the median, the data should be arranged in order from least to greatest. If there is an even number of items in the data set, then the median is found by taking the mean (average) of the two middlemost numbers.
So 5 and 6 are the middle you add the then divide by 2
the expression is 3(15+7). An word problem could be there are 15 apples and 7 bananas. Someone needs to buy 3 times the amount of those. This is represented by that expression.