"Benny needs your help protecting frank's territory"
for this mission, you need to head over to Phalanx Casino, one of frank's places. Apparently, according to Benny at least, a host of cartel thugs are heading there to Heist it. You only have two minutes to get there, so get a car and step on it. You should have plenty of time to get there in reality, so don't worry if you get the route a little wrong.
Upon arrival, Benny is waiting for you. Some bikers will arrive first of all. Luckily, Benny has given you an assault rifle which makes dealing with them very easy. Soon after, enemy reinforcements will appear behind you and you will need to take them out. After that, you'll have to face one final set of enemies, on the other side of you, before Benny confirms that you've got them all and the mission is completed.
Reward: G170,000, Respect: 735,000