Used 6 cups of whole wheat flour and x cups of white flour in the recipe. what is the equation that can be used to find the value of y, the total amount of flour that otto used in the recipe, and what are the constraints on the values of x and y? d

Total number of cups of flour used is

T(x) =    6 cups (whole wheat flour) + x cups (white flour)

Question is not very clearly worded.  Is '6 cups' a special value for y, the number of cups of whole wheat flour used?

If so, then 

Total flour used = y + x (cups)

Constraints:  x and y are constrained to be zero or greater.  Of course, there are practical limits on how large a batch of this recipe is to be made.  We could state, arbitrarily, that neither x nor y may exceed 20 cups.