Question 321168
Let Carlos's speed be x mph
Elena bicycles 6km/h faster . x+6 mph
Carlos cycles 27km, 
Elena can bicycle 45km. in the same time.
time taken by carlos = time taken by Elena
27/x = 45 / x+6
45x=27(x+6)
45x=27x+162
45x-27x=162
18x= 162
x= 162/18
x=9 mph - Carlos'speed.
15 mph will be Elena's speed.