Hints: Line – B second line. Explanation:

D^2= 3^2 + 6^2 => 9+36 => 45
C^2= 5^2 + 5^2 => 25+25 => 50
B^2= 6^2 + 4^2 => 36+16 => 52
A^2= 7^2 + 1^2 => 49+ 1 => 50