A = W· L
10,000 = W ( W +30 ) = W² + 30 W
W² + 30 W - 10,000 = 0
W =

L = 86.12 + 30 = 116.12
Width of a plot is 86.12 m and lenght is 116.12 m.
Check : A = 116.12 · 86.12 ≈ 10,000
The question is worded a bit strangely (in my opinion anyway), but I think your teacher wants you to describe how exponents work.
Let's say we had the expression 
The base is 5 as its the bottom most value (think of something like the base of a tree or building). The exponent is 3.
The exponent of 3 tells the reader to multiply the base 5 by itself 3 times like so

With larger exponents, it becomes more tedious to write out all the repeated multiplications, which is why many calculators have an exponent button to save time.
So the amount needed=area of circle times height
area formula=pi times radius^2
height=3/4
so
pi=aprox 3.14
radius=7
3.14 times 7^2
3.14 times 49
153.86
times 3/4
115.395 in^3
answer is 115.4 cubic inches