On Saturday morning Lynn walked for 2 hours and then ran for

On Saturday morning, Lynn walked for 2 hours and then ran for 30 minutes. If she ran twice as fast as she walked and she covered 12 miles altogether, then how fast did she walk?

rt=d
w*2+r*1/2=12
r=2w
r=8 w=4
check
2*4+4=12
12=12