Y=10x select the answer showing the ratio x:y

The pyramid below was dissected by a horizontal plane which shape describes the pyramid horizontal cross section

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.  

3.4a=57.8 what is the the value of a