first bonus missions

[Razorflame]

hi i'm pretty new to the game and playing on hard(i am an experienced gamer and i play everything on hardest possible mode)

anyway
how the hell can u complete this quest on hard
(i think it's called the apprentice and the mage or something)

anyway u have to defend 15 turns O.o

you have like 4 militia 3 spearmen 3 eyoen bowmen a battle mage crow master maverick and master brennok

and u have to battle like

3 battle priest(all level 3)
7 landles horseman
4 champions of norath
1 warrior of nortah
a balista
4 crosbowmen
1 bowman
1 scout
1 assasin

and it's so hard to beat this level

i can beat the first 2 waves of them
but the third wave always managed to get into my town and then i fail

got any tips on this level?
^^