Answer:
The coordinates of point B is (8,-4)
Step-by-step explanation:
Midpoint of a line segment: It is the point on the line segment that divides the segment in two congruent segments.
Since it is given that C is the midpoint of Line segment AB.
Mid-point of a segment of end points
and
is, C=
.
As, given the coordinates of A and C are (2,4) and (5,0)
then, we have
,
;
and 
to find the coordinates of
.

Simplify:

⇒ 
to solve for
we have, 
or
or
= -4
so, the values of
and 
Therefore, the coordinates of point B is (8,-4)