Which system is equivalent to startlayout enlarged left-brace 1st row 5 x squared + 6 y squared = 50 2nd row 7 x squared + 2 y squared = 10 endlayout? startlayout enlarged left-brace 1st row 5 x squared + 6 y squared = 50 2nd row negative 21 x squared minus 6 y squared = 10 endlayout startlayout enlarged left-brace 1st row 5 x squared + 6 y squared = 50 2nd row negative 21 x squared minus 6 y squared = 30 endlayout startlayout enlarged left-brace 1st row 35 x squared + 42 y squared = 250 2nd row negative 35 x squared minus 10 y squared = negative 50 endlayout startlayout enlarged left-brace 1st row 35 x squared + 42 y squared = 350 2nd row negative 35 x squared minus 10 y squared = negative 50 endlayout.