First, convert 3 3/4 hours into an improper fraction for easier computation. Thus, we get 15/4
1.) 15km : 15/4 hr = x km : 1/2
15/2 = 15x/4
x = 8 km
2.) Again, convert 1 1/6 into an improper fraction, yielding 7/6
15km : 15/4 hr = x km : 7/6 hr
(15)(7)/6 = 15x/4
x = 28/6 hr = 14/3 hr = 4 2/3 hr = 4 hrs, 40 min
Hope this helps :)