Suppose r(t) = cos(t)i + sin(t)j + (3t)k represents the position of a particle on a helix, where z is the height of the particle. (a) What is t when the particle has height 12? (b) What is the velocity of the particle when its height is 12? (c) When the particle has height 12, it leaves the helix and moves along the tangent line at the constant velocity found in part (b). Find a vector parametric equation for the position of the particle (in terms of the original parameter t) as it moves along this tangent line.