Answer:
96 inches
Step-by-step explanation:
The answer is 6$ because 50% of 40 would be 20 and 50% of 20 is 10 but when you all on the tax which would be around a dollar when you take 50% of 10 which is 5 and add on the tax which is a dollar you then get 6$ in total.
To find this answer, we need to multiply 3.57 by 12.

Therefore, 12 planks will cost $42.84.
a geometric sequence is a bunch of numbers where you can get from a number to the next number by multiplying the previous number by a certain number
might be confusing so here's an example
1,2,4,8,16
each term is multiplied by 2 to get next term, that number that each term is multiplied by is called the common ratio
formula for geometric sequence is

where
is nth term
is first term
r is teh common ratio
n=which term
in our example
1,3, 9, 27, 81
each term is being multiplied by 3 so it is a geometric sequence and thus r=3
also first term is 1 so 
so the formula is
or in function notation 