Isent that problem before somebody me with it and got theta=45 degree, but it was wrong. even though, i really appreciated he's hard work. i reposted it again in case if somebody else would be able to me.

your medieval history class is constructing a trebuchet, a catapultlike weapon for hurling stones at enemy castles. the plan is to launch stones off a 71- m -high cliff, with initial speed 39 m/s . some members of the class think a 45 ∘ launch angle will give the maximum range, but others claim the cliff height makes a difference. what do you give for the angle that will maximize the range?