Convert 8cm and 12cm to 80mm and 120mm. A=(width)(length) so A=(80)(120) which equals 960mm^2.
1/4 + 1/4 + 1/4 is the sum of unit fraction, there are 3 unit fractions
900 is the correct answer
9/27, 12/27, 16/27
So this is a geometric sequence as each term is 4/3 the previous term.
Since the common ration is greater than one the sum of the series diverges, it does not exist. (The sum just keeps getting larger and larger)
For a geometric series to have a sum r^2<1
So that the normal sum....
s(n)=a(1-r^n)/(1-r) becomes if r^2<1
s=a/(1-r)