A hectare is 10,000 square metres. Map scales are linear so 1cm measure on a map is equivalent to 25,000cm. Since there are 100cm to a metre 25,000cm=250 metres. 1 square cm is equivalent to 250*250 square metres = 62,500 sq metres. A map area of 11.5 sq cm is therefore equivalent to 11.5*62500=718,750 sq m. Divide this by 10000 and we get the area in hectares: 718750/10000=71.875 hectares. That rounds up to 72 hectares.