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

On Saturday morning John walked for 2 hours and then ran for 30 minutes. Is he ran twice as fast as he walked and he covered 12 miles altogether, how fast did he walk

Let w = John\'s speed walking
r = John\'s speed running

Since distance = speed * time, then:
2w + (0.5)r = 12
r = 2w
Substituting 2w for r, we get
2w + (0.5)(2w)=12
3w = 12
w=4
r = 2(4)
r = 8
Therefore, John walks at 4mph and runs at 8mph