Further mechanics question

so i did this question,
The total mass of a cyclist and his bicycle is 100kg.
In all circumstances, the magnitude of the resistance to the motion of the cyclist from non-gravitational forces is modelled as being kv^2
N, where vms−1 is the speed of
the cyclist.
The cyclist can freewheel, without pedalling, down a slope that is inclined to the horizontal at an angle α, where sinα =1/35 , at a constant speed of Vms−1
When he is pedalling up a slope that is inclined to the horizontal at an angle β, where sinβ =1/70 , and he is moving at the same constant speed Vms−1 , he is working at a constant rate of P watts.
(a) Find P in terms of V.
(7)
If he pedals and works at a rate of 35V watts on a horizontal road, he moves at a constant speed of Ums−1
(b) Find U in terms of V.
I got both parts correct but only scored 3/4 on part B as the mark scheme says only 3/4 marks awarded if you find U using the cube root of 5/4 V as it depends on the use of g, but the method they used also uses g so i'm a little confused
this is the link to the markscheme (its question 3b)
https://www.physicsandmathstutor.com/pdf-pages/?pdf=https%3A%2F%2Fpmt.physicsandmathstutor.com%2Fdownload%2FMaths%2FA-level%2FPapers%2FEdexcel-Further%2FMechanics-1-AS%2FMS%2FJune%202021%20MS%20.pdf