What expression is equivalent to 13-(-21)?

Otto used 6 cups of whole wheat flour and cause 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 his recipe and what are the constraints on the value of x and y? a y=6x; x is any interger greater than the equal to 0 and y is an interger greater than the equal to 6? b y=6x; is any real number greater than or equal to 0 and y is any real number greater than or equal to 6? c y=+6; x is any intger greater than or equal to 0 and y is an intger greater than or equal to 6? d y=x+6; x is any real number greater than 0 eqaul to 0 and y is any real number greater than or eqaul to 6? [someone answer this with a b c or d simplyactaully answer it this took forever to type on my phone] you. ill even raise the number of points get