f:=x*(1-1/(2*3.14159)^(1/2)*(exp(-(log(x/(0.96*426458))/y+y/2)^2/2))*(0.31938153*1/(1+0.2316419*(log(x/(0.96*426458))/y+y/2))-0.356563782*(1/(1+0.2316419*(log(x/(0.96*426458))/y+y/2)))^2+1.781477937*(1/(1+0.2316419*(log(x/(0.96*426458))/y+y/2)))^3-1.821255978*(1/(1+0.2316419*(log(x/(0.96*426458))/y+y/2)))^4+1.330274429*(1/(1+0.2316419*(log(x/(0.96*426458))/y+y/2)))^5))-0.96*426458*(1-1/(2*3.14159)^(1/2)*(exp(-((log(x/(0.96*426458))/y+y/2)-y)^2/2))*(0.31938153*1/(1+0.2316419*(log(x/(0.96*426458))/y+y/2))-0.356563782*(1/(1+0.2316419*(log(x/(0.96*426458))/y+y/2)))^2+1.781477937*(1/(1+0.2316419*(log(x/(0.96*426458))/y+y/2)))^3-1.821255978*(1/(1+0.2316419*(log(x/(0.96*426458))/y+y/2)))^4+1.330274429*(1/(1+0.2316419*(log(x/(0.96*426458))/y+y/2)))^5))=34170:

g:=y=0.3023*34170/(x*(1-1/(2*3.14159)^(1/2)*(exp(-(log(x/(0.96*426458))/y+y/2)^2/2))*(0.31938153*1/(1+0.2316419*(log(x/(0.96*426458))/y+y/2))-0.356563782*(1/(1+0.2316419*(log(x/(0.96*426458))/y+y/2)))^2+1.781477937*(1/(1+0.2316419*(log(x/(0.96*426458))/y+y/2)))^3-1.821255978*(1/(1+0.2316419*(log(x/(0.96*426458))/y+y/2)))^4+1.330274429*(1/(1+0.2316419*(log(x/(0.96*426458))/y+y/2)))^5))):

fsolve({f,g},{x,y},{x=400000..1000000,y=0..5});