Answer:the cost of a small box of tangerine= $11 and the cost of a large box of tangerine= $19
Explanation:
Step 1
Let price of small box of tangerines be represented as x
 and price of large box of tangerines be represented as y
 Such that the equqtion for Brenda who sold 12 small boxes of tangerines and 1 large box of tangerines for a total of $151 be represented as 
12x + y = 151--------equation 1
and 
the equation for Cody who 1 small box of tangerines and 3 large boxes of tangerines for a total of $68
 x + 3y= 68-------equation 2
Step 2 
12x + y = 151--------equation 1
 x + 3y= 68-------equation 2
 By eliminaton methd multiply equation 2 by 12
 x + 3y= 68-------equation 2 x (12)
12x + 36y=816 --------equation 3
 Subtract equation 1 from equation 3
12x + 36y=816 --------equation 3
-12x + y = 151--------equation 1
35y=665
y=665/35 =19
 to get x , we substitute the value of y=19 into equation2 
 x + 3y= 68
x+ 3 x 19=68
x=68-57
x=11
Therefore the cost of a small box of tangerine= $11 and the cost of a large box of tangerine= $19