let x be the speed of bicyclist A (heading north)
y be the speed of bicyclist B (heading south)
since A is 5km/hr faster than B
x = y + 5 -----equation 1
time = 9 to 10:45
= 1.75hours
since the distance is 47.25km then,
x(1.75) + y(1.75) = 47.25 ---equation 2
substitute equation 1 to 2
(y+5)(1.75) + 1.75y
= 47.25
1.75y +8.75 + 1.75y
= 47.25
3.5y
= 47.25 - 8.75
3.5y
= 38.5
y = 11km/hr
substitute to equation 1
x = y + 5
x
= 11 + 5
x
= 16km/hr