Angle theta required to hit coordinate (x,y) based on http://en.wikipedia.org/wiki/Trajectory_of_a_projectile#Angle_required_to_hit_coordinate_.28x.2Cy.29

MathHelper.cs

using using UnityEngine;
using System.Collections;
using System.Collections.Generic;

class MathHelper {
  float static CalcAngleOfElevation (Vector3 from, Vector3 to, float v, float g) {
		float x = (to - from).z;
		float y = (to - from).y;
		float v2 = v * v;
		float v4 = v2 * v2;
		float fac = v4 - g*(g*x*x + 2*y*v2);
		if(fac < 0) {
			return Mathf.Infinity;
		}
		float theta = -Mathf.Atan((v2-Mathf.Sqrt(fac))/(g*x)) * Mathf.Rad2Deg;
		while(theta < 0) theta += 360f;
		return theta;
	}
}