The answer is A). Five people received the email on the first day on the experiment.
Answer:
I think it's B, I might be wrong though

Formula :
Base²= Hypotenuse² - Perpendicular ²












Remember the a² in formula has nothing to do with the a we have to find. :)
We know that
<span>Vertex (0, 0) and directrix y = 4
is a vertical parabola------> open down (directrix above the vertex)
the equation is of the form
(y-k)=4p(x-h)</span>²--------> y=4p*x²-------> vertex (0,0)
y=4
y=h-p-----> y=-p
p=-4
the equation of the parabola is
y=-16x²
the answer isy=-16x²
see the attached figure