I'm very unfamiliar with this 'radius of gyration', so I just kind of plugged the values in without much awareness.

I get I = 0.24^2*12.5, with I as the mass moment of inertia.

Then did

F= ma, and set equal to the unknown times the distance to the hip flexors

0.58*18*0.24^2*12.5 = 0.42*x

then solved for x.

Is this right, or am I just way off?

Any help would be appreciated.

EDIT: Okay, I've got some more information, and I think I'm way off with the second part: