Calculate Distance Between two Game objects

Hello
I am here finding group of sphere of same tag…

For that oncollision , i have got array of all the sphere which are in contact of collided sphere…

Method i have used : var hitColliders = Physics.OverlapSphere(collision.transform.position, 0.6);

By this method , I am getting group of sphere connected to each other.
But i want to find the closest sphere among this array. So i need to calculate the distance between bullet sphere and all the game objects within this array.
From that i want to find minimun distance object.

But i am not getting the way to calculate distance??
Please Help me out. Thanks in advance for ur support and help…

vector3.distance(sphere1.transform.position,sphere2.transform.positon)

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