Who is at fault if car a is mergeing into the next lane hit car b and caused car b to hit car c then car a hits car b again car c is injured who pays for car h's injuries?

Who is at fault if car a is mergeing into the next lane hit car b and caused car b to hit car c then car a hits car b again car c is injured who pays for car h's injuries?
H is. Why is it there in the first place. You can see there is another car there, so get out the way