Explanation:
Obviously, this specific question can be answered by multiplying the lengths by 10 and taking the greatest common divisor, but the general question is more interesting. For example, the preceding method will not work if the dimensions are irrational.
The general method is to express the ratio of length and width as a reduced fraction. This is possible even if the dimensions are irrational, provided that their ratio is rational. (If their ratio is irrational, the problem is possible if it is to subdivide into rectangles with a suitably chosen, irrational ratio of its two dimensions.)
In the present case,
9.8/7.2=49/36,
so there are 49 squares across and 36 squares in the other direction. The size of the square is
x by x=9.8/49 by 7.2/36=0.2 by 0.2 kilometres.