3x^2 - x - 10

when this trinomial is factored completely, one of its factors is
a) x + 2
b) x - 5
c) 3x + 5
d) 3x - 2

Parabolas y=−2x^2 and y=2x^2+k intersect at points a and b that are in the third and the fourth quadrants respectively. find k if length of the segment ab is 5.