Penalty Enforcement

[my3sons]

A's ball on their on 3 yard line. A1 fumbles the ball in the end zone. A2 then intentionally kicks the ball illegally out the back of the endzone into deadball territory. Other then B getting 2 points for the safty, what would be the penalty enforcement for this situation?
If B accepts the penalty would it be enforced from the 20 yd line which would be half the distance to the goal. Please only answers that you can back up with a rule or casebook quote. By the way Fed rules.