If the quantities of two solutions are x (25%) and y (50%) then x+y=9 litres.
Also 0.25x+0.5y=0.4*9=3.6 for quantities of pure HCl. So we can substitute y=9-x:
0.25x+0.5(9-x)=3.6, 0.25x+4.5-0.5x=3.6, 0.9=0.25x, x=3.6L and y=5.4L.
She needs 3.6L of 25% solution and 5.4L of 50% solution.