6 teaspoons 
3/4 * 8 is 24/4
24/4= 6
So you need 6 teaspoons
        
             
        
        
        
Answer: 3,19 which is larger than the original
Step-by-step explanation: if you consider that the original average is 3 you can say that all 25 students have 3 siblings so the average is 3, if you add another students with 8 siblings and do some math (25*3+8)/26 its 3,19