Question 1152688
let s = Dave's speed
Katie bikes 6mph faster than Dave.
(s+6) = Katie's speed 
 Katie can bike 11 miles in the same amount of time that Dave can bike 8 miles.
write a time equation; time = dist/speed
{{{8/s}}} = {{{11/((s+6))}}}
cross multiply
11s = 8(s+6)
11s = 8s + 48
11s - 8s = 48
s = 48/3
s = 16 mph is D's speed
then
16+6 = 22 mph is K's speed
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Check, find the time of each
8/16 = .5 hrs
11/22 = .5 hrs