Answer:
Step-by-step explanation:
Given
Suppose side face have a dimension of l\times l
and width of h
volume 

volume 
Area of side wall is 
Area of top Wall 
Area of bottom 
Cost of bottom wall 
Cost of top wall 
Cost of side walls 
total cost 


differentiate C w.r.t l to get minima or maxima






Dimension of Box is 
Y= -x + 2 and y= 3x - 4
As these both equal y, you know that they both equal each other so
-x + 2 = 3x - 4
Third option :)