To find out how many Salmon Filet's were served, knowing that 80% of the specials were Salmon Filet, and there were a total of 70 specials in total, we need to find what 80 percent of 70 is. That's because that will lead us to our answer.
Since a percent is something over 100 (per 100), 80% is 80/100 which simplifies to 4/5. That means that we have to multiply 70 by 4/5. 70 * 4/5 is equal to 280/5. Since 280/5 equal 56, there were 56 Salmon Filet's served, or C.