The correct option is D 13
The roots of equation x2+5x+7=0 are non-real. And we know that if a quadratic equation with real coefficients have non real roots, then they occur in conjugate pair.
We are given that the both equations have a common root and a,b,c are natural numbers. It means the roots of the equation ax2 + bx + c = 0have complex roots in conjugate pair. Thus, the both equations have both common roots.
So, a1= b 5=c7=k, k∈N⇒a=k, b=5k, c=7k⇒a+b+c=13kHence, the minimum value of a+b+c is 13