Part 1)
we know that
The Centroid of a Triangle is the centre of the triangle that can be calculated as the point of intersection of all the three medians of a triangle.
The Centroid divides each median into two segments whose lengths are in the ratio

so


we have

substitute

Find RZ


therefore
the answer Part 1) is the option C

Part 2)
Statements
case A) ∠BEC is an exterior angle
The statement is False
Because, ∠BEC is a internal angle
case B) ∠DEC is an exterior angle.
we know that
An exterior angle is formed by one side of a triangle and the extension of another side
therefore
The statement is True
case C) ∠ABE and ∠EBC are supplementary angles.
we know that
∠ABE+∠EBC=
-------> by supplementary angles
therefore
The statement is True
case D) ∠BCF and ∠BEC are supplementary angles
The statement is False
Because
the only way that is true is that the triangle BEC is isosceles and that the ∠BEC is equal to the ∠BCE
case E) ∠BEC is a remote interior angle to exterior F.∠BCF
we know that
Remote interior angles are the interior angles of a triangle that are not adjacent to a given angle. Each interior angle of a triangle has two remote exterior angles.
In this problem ∠BEC has two remote exterior angles (∠BCF and ∠EBA)
therefore
The statement is True