Question 47900
Right then, this is better done with algebra, which is no doubt why you posed the question here.


Let the speed of the wind be w.
Then Jeanie's speed with the wind is 33+w.
And Jeanies's speed against the wind is 33-w.


Then, the time Jeanie bikes 75km against the wind is 75/(33-w)
And also, the time Jeanie bikes 123km with the wind is 123/(33+w)
which, as the question says, is the same.
Therefore, 
75/(33-w) = 123/(33+w)
which becomes, after cross multiplying
{{{ 75(33+w) = 123(33-w) }}}
which becomes
{{{ 2475 + 75w = 4059 - 123w }}}
which becomes
{{{ 198w = 1584 }}}
which means w = 1584/198 = 8
And thus, putting back the units, we have the speed of the wind is 8 km/h