If real numbers x and y satisfy x · x + XY + y = 14 and Y · y + XY + x = 28, then the value of X + y is equal to

If real numbers x and y satisfy x · x + XY + y = 14 and Y · y + XY + x = 28, then the value of X + y is equal to

Add the two expressions to get the
(x²+2xy+y²)+(x+y)-42=0
That is, (x + y) & sup2; + (x + y) - 42 = 0
So [(x + y) + 7] [(x + y) - 6] = 0
So x + y = - 7 or x + y = 6