Area Of Triangle:
4/2 = 2
2x6 = 12
12x2 = 24ft^2
Remaining area:
150 - 24 = 126ft^2
Maximum length:
126/6 = 21
x = 21ft
Ok, to show that she is incorrect we can use any other number in both equations and they will not be equal. the number she used does turn out equal but that does not mean the equations are equal.
for example
2 times 3=6
3 to the power of 2 is 9
that shows the expressions are not equal
Four positions of such a sequence are given to be 3s, and we have 10 choices for the remaining eight positions. So the number of such sequences is

or 100 million.
It seems that you have missed the necessary options for us to answer this question, but anyway, here is the answer. Based on the given scenario above about what Annabelle did, the kind of statistical investigation that she performed was a SURVEY. Hope this helps.
If I did this right it should be 8.