Option D is the correct answer.
Step-by-step explanation:
Step 1 :
Let A represent the cost of one bucket of apple and P represent the cost of one bucket of peaches.
So we have , 
4 buckets of apples and 5 buckets of peaches for $64
8  buckets of apples and 3 buckets of peaches for $72
Writing this in the equation form we have,
4A + 5P = 64
8A + 3P = 72
Step 2:
Solving for the above 2 equations we can get the required costs 
Equation 1 is 
4A + 5P = 64 , Multiplying this by 2 we have 8A + 10P = 128 
Equation 2  = 8A + 3P = 72
Subtracting both we have , 7p = 56 = > P = 8
Substituting this in equation 1 we have 
8A + 80 = 128 => A = 6
Hence the cost of one bucket of apple is $6 and the cost of one bucket of apple is $8.
Option D is the correct answer.