In this problem, we must first calculate that Ellen will be on air. Using the equation of a free-falling body,
y = -g/2*t^2 + y0
When she hits the ground, y = 0. With y0 = 7 and g = 9.80,
0 = -4.90*t^2 + 7
t = 1.20 s
Thus, her horizontal displacement is then
x = vt
x = (12)(1.20)
x = 14.3 m