So I don't remember how to do IQR or MAD but I can help you with the rest for the garter snake (hopefully I'll explain it well enough so that you can do the water snake on your own.
Mean: Add all the numbers together then divide the sum by the number of integers given
26 +30+22+15+21+24+28+32+24+25+18+35 = 300
If you count there are a total of 12 numbers so you have to divide 300 by 12
300 / 12 = 25
Median: Put the numbers in order from lest to greatest then find the number in the middle
^^^What I do for this is start on the out side and take away one on both sides each "round" until I reach the middle (Does that make sense?)
15 18 21 22 24 24 25 26 28 30 32 35
18 21 22 24 24 25 26 28 30 32
21 22 24 24 25 26 28 30
22 24 24 25 26 28
24 24 25 26
24 25
^^^Now this is tricky because there are two number remaining instead of one, so you have to find which number is in between the two left. This one is easy (the middle of 24 and 25 is 24.5) since they are only one number apart, but if it is more difficult what you do is take the mean of those two remaining numbers
24 +25 = 49
49 / 2 = 24.5
Mode: Which number appears the most often in the set of data?
15 18 21 22 24 24 25 26 28 30 32 35
24 appears two times in the data where the rest of the numbers appear only once therefore 24 is the mode of this set of data
Range: Subtract the largest number by the smallest number
Largest number: 35
Smallest number: 15
35 - 15 = 20
Hope this helpd!