Since you are standing back to back you will add the distances you ran forward.
12+16=28.
Since your right is different than your friend's right you also add that together.
12+9=21.
Those are the 2 side lengths of an imaginary triangle. To find the hypotenuse simply use the equation a^2+b^2=c^2.
Plug the numbers in.
28^2+21^2=1225
Find the square root.
=35
So, you threw the ball 35 feet to your friend.