The reminder is one degree less than the divisor. So it is in the form mx + b. Note P(X) = (x-2)*(x+3)*Q(X) + mx + b where Q(X) is the quotient
2m + b = 4 # Since the divisor = 0 when x = 2
-3m + b = 9 # Since the divisor = 0 when x = -3
5m = -5
=> m = -1
=> b = 6