To win this fight you must defeat Gary and Helen. Gary comes out first. Just fire off N60 shots and he'll quickly withdraw and Helen will take his place. Deal with her the same way, jumping over the electric shockwaves she releases. If too slow, she jumps close to you while swinging the whip that can do nasty damage. She withdraws eventually, leaving you to deal with Gary who will let off a barrage of missiles. Keep moving with the Thruster-Pack. Helen will switch in where you will kill her. As well as her attacks however, you have to deal with Gary's missiles. Once she dies, just take out Gary's remaining health and 4000 bolts is yours.