Let Zhang Qiang walk X every hour and Yi Lee walk Y every hour.

0.5x+2x+2y=20

x+y=20- 1 1

that is

2.5x+2y=20

x+y=9

X=4 and y=5 are obtained by simultaneous solution.

A: Zhang Qiang walks 4 kilometers per hour and Li Yi walks 5 kilometers per hour.