People moved to the cities to escape war. Some people had left the countryside to work in the arms industry and some had left for Rome looking for subsistence. Rome became the most populous city in Europe and West Asia.
If you are solving for c:
c + 3/4 = 5/4
5/4 - 3/4 = c
c = 2/4 or 1/2
There are several ways. A very good way is gaussian elimination.
The square root of 729 is in fact 27, as it is a perfect square, but this is not well known, so we can figure it out like this:
What goes into 729 that are perfect squares? 81 and 9:
Take the square root of 81 (9) and the square root of 9 (3). Move these to the outside of the square root (they will multiply with 3 since 3 is multiplied to the square root in the original problem)
Now, just multiply: