Answer:
76
Explanation:
the second number = the first one + 3
the third number = the second one + 5
the fourth number = the third one + 7
the fifth number = the fourth one + 9
because of this, we can know that we add an odd number to the left number
so
sixth = 20+11=31
seventh = 31+13=44
eighth = 44+15=59
ninth = 59+17=76