Please find the attachment below. Thanks
Regarding a): the vertical component of the 'force at F' equals -3 kN. (I assume it was just a typo, since you used -3 kN in b).)
Regarding c): how to replace a force and a moment with a resultant force (if I got that right)? Well, the resultant force must equal the force F, and the distance d between that resultant and the 'old' resultant force must be chosen so that F*d = M, i.e. it is replacine the moment M now, too. Further on, the 'direction' of the moment F*d must equal the 'direction' of the moment M.
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