To find the average of 4 things, we add those four things together and divide by 4. So, here we need to do the opposite. Since the last thing we would do to find the average is divide by four, we are going to start there and do the opposite. The average is 166. So...
166X4=664
Now instead of adding, we will subtract the three that we know, leaving the fourth. 664-200=464 464-150=314 314-180=134
