(2)P→Q P (additional premise)

(3)(P→(Q→R)) P

(4)Q→R T( 1)，(3)I

(5)P→R T(2)，(4)I

(6)R T( 1)，(5)I

(7)P→R CP

(8)(P→Q)→(P→R) CP

The first answer is for encouragement _