Let the no of the correct answer be x than marks he got for a correct answer be 4x.
No of wrong answers and unanswered be (180-x) marks deducted be -1(180-x) now total marks = 450
=> 4x -(180-x) = 450
=> 5x = 450 +180
=> 5x = 630
=> x= 630/5
=> x= 126