Answer
$$0.675 \ ha.$$
Work Step by Step
The area of the field is $$75 \times 90 m^2=6750 \ m^2.$$
Now change it to $ha$ by dividing by $10^4$; that is:
$$6750 \ m^2= \frac{6750}{10^4}\ ha =0.675 \ ha.$$
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