On monday,there were thrice as many peanuts in Sack X as Sack Y.On tuesday,3952 peanuts in Sack X were sold.Now there were thrice as many peanuts in Sack Y as Sack X.How many peanuts were there in Sack X at first?

Let the number of peanuts in sack Y = P
So, the number of peanuts in sack X=3P
Now, 3952 peanuts were sold from sack X. So, left peanuts in sack X = 3P-3952
According to question,
3(3P-3952) = P
9P - 11856 = P
9P - P = 11856
8P = 11856 
P =11856/8  
P = 1482
Thus, the number of peanuts in sack Y = 1482
And, the number of peanuts in sack X = 3*1482 = 4446