Michael has to walk 3/8 of a kilometer tyo the store. he walks 4/5 of the way. how far did he walk?

The first thing you should do for this case is find the amount that Michael has traveled.
 For this we have to multiply the distance to the store and the percentage traveled.
 We have then:
 (3/8) * (4/5) = 12/40
 Simplifying we have:
 (12/40) * ((1/2) / (1/2)) = (6/20) * ((1/2) / (1/2)) = 3/10
 answer
 Michael has walked 3 / 10Km (80% of the way to the store)