first put them in sequential order so it would be
10, 10, 15, 15, 16, 18, 23
okay Then, divide the sequence into the 1st and 3rd quartiles. the median would be 15 becuase it is the middle.
1st - 10
3rd - 18
then you subtract
18 - 10 = 8
your answer is 8 this should help you with your other ones hope this helps you