Mode : the quantity that appears the most in a sequence
Because 7 is the number that appears the most ( 3 times ), it is the mode.
Range : the difference between the largest number and the smallest number
In this case, 12 is the biggest and 7 is the smallest -> Range = 5.
Median : the "middle number" (for example, if the sequence has 7 numbers, the 4th number will be the median. if the sequence has 8 numbers, the median will be the average of the 4th and 5th number, and of course from increasing order.)
There are 8 numbers in the sequence, from lowest to highest : 7,7,7,8,10,11,12,12.
So, the median = (8+10)/2 = 9.