Calculate the pH with the given ka values

Given the following ka values for citiric acid, calculate the pH and the concentration of the citrate tianion(C₆H₅O₇ ^3-) in a 0.10 M solution of citric acid: k_a1= 7.4 x 10 ^-4; k_a2= 1.7 x10^-5; k_a3= 4.0x 10 ^-7.