Clear[Evaluate[Context[]<>"*"]];
k[x_]:=faktor/x;
eqns={
xI==(xSteps-1)(x-xStart)/(xStop-xStart),
verh==xStart/(xStop-xStart)
}
xStart=xStart/.First@Solve[eqns[[2]],xStart];
kI=(xSteps-1)(k[x]-k[xStop])/(k[xStart]-k[xStop]);
kI/.First@Solve[eqns[[1]],x]//FullSimplify
xI/.First@Solve[kIi==%,xI]//FullSimplify