We investigate solutions of Witten-Dijkgraaf-E.Verlinde-H.Verlinde (WDVV) equations. The article discusses nonlinear equations of the third order for a function f = f(x, t)) of two independent variables x, t . The solution of some cases of hierarchy equations of associativity illustrated. Lax pairs for the system of three equations, that contains the equation of associativity are ...