Answer:
43
Step-by-step explanation:
<img src="https://tex.z-dn.net/?f=258%3D240%2B18%5C%5C%5C%5C258%3A6%3D%28240%2B18%29%3A6%3D240%3A6%2B18%3A6%3D40%2B3%3D%5Cboxed%7B43%7D" alt="258=240+18\\\\258:6=(240+18):6=240:6+18:6=40+3=\boxed{43}"/>
