To find the Area of a quadrilateral, you always multiply Length * Width. In the case of a square, all sides are the same length, so you simply multiply 65.5* 65.5. The reason you can use 65.5 is that there are 10 decimeters in one meter, so if you convert decimeters to meters you have 5/10 of a meter.
This is a two-step problem. After you have found the Area of the square, you must then subtract it from 10,000 which is how many square meters are in a hectare.
Your problem will look like this:
65.5*65.5 = A of square
10,000 - A = X sq meters
65 m 5 dm
convert the dm into meters. There are 10m in 1dm so just divide the 5 by 10
5dm / 10 = .5 m add it to 65m
65 + .5 = 65.5 m
to find the area of the square, multiply 65.5 by itself:
65.5 x 65.5 = y meters squared
10,000 - y = h
65m 5dm is the same as 65.5m.
To find the area of a square you multiply two of its sides...
So the area of your square is...
65.5 x 65.5 = X m.sq.
A hectare is a unit of area equal to 10,000 m.sq
So your answer will be 10,000 - X and the units will be Square Meters