Anne and Mark purchased three-fourth of 1250 hectares plot for large scale farming purposes.
3/4 * 1250 = 937.5 hectares
3 months later, they decide to let a fifth of their purchased land be used by a nearby construction
1/5* 937.5 = 187.5 hectares
937.5 - 187.5 = 750 hectares
Since 1km^2 = 100 hectares
100 h / 100 = 1 km^2
750 h / 100 = 7.5 km^2