Answer
3/4.
Work Step by Step
The hose is horizontal. If the water lands 4 times farther away, then the initial horizontal speed has increased by a factor of 4, because the time in the air is the same. Apply the equation of continuity to find the change in the hose opening. The water has the same volume rate of flow before and after. Let 1 represent before, and 2 represent after.
$$A_1v_1=A_2v_2$$
$$\frac{A_2}{A_1}=\frac{v_1}{v_2}=0.25$$
The final area is one-quarter the initial area, so 3/4 of the opening was blocked.