Let t=time it took Kwan to go up the hill
Then 3-t=time it took him to go down the hill
Distance(d) equals Rate(r) times Time(t) or d=rt; r=d/t and t=d/r
distance up the hill = distance down the hill
distance up=4*t
distance down=6*(3-t)----So:
4t=6(3-t) get rid of parens (distributive law)
4t=18-6t add 6t to both sides
4t+6t=18-6t+6t collect like terms
10t=18 divide both sides by 10
t=1.8 hr---------------------------------time to go up the hill
3-1.8=1.2 hr-----------------------------time to go down the hill
Hope this helps
