Posted by Amy on Sunday, April 10, 2011 at 2:54pm.
-16t^2 + 64t - 42 = 0
Divide end values into two factors (-7,6 or 7,-6, or 21,-2 or -21,2 or 14, -3 or so on) (16,-1 or -16,1 or 4,-4 or -8, 2 and so on) to see how their sum will get the center value.
From there it is trial and error. Start trying.