应该是：
It's thirty square meters in area
Its area is thiry square meters有某人正做某事翻译应该是： sb is doing sth现在进行时， .~~~~~~~~~~～～~~~~祝你进步，如对你有帮助，请及时采纳~~~~~~~~~~~~~~~~能不能There be sb doing sth 还是There has sb doing sth　人可以直接做主语，没必要用there　be 句型