in a 0.1 M phosphate buffer solution with pH 4, the total concentration of phosphate species (both the acid and the conjugate base) is 0.

in a 0.1 M phosphate buffer solution with pH 4, the total concentration of phosphate species (both the acid and the conjugate base) is 0.1 M. If x is the concentration of conjugate base in the buffer solution, what is the concentration of the acid in terms of x?