How do i find the length and the width?

Find the perimeter of the triangle with vertices  d(3, 4),  e(8, 7), and  f(5, 9). do not round before calculating the perimeter. after calculating the perimeter, round your answer to the nearest tenth.  

Pleas ! i just cant seem to get it right! choose: congruent or proportional choose: cf or ce or bc choose: segment addition postulate or cpctc

What is the midpoint of np if n (1,9) and p (-5-1)