a. 15, 21 . it adds one more than the previous number added so, +1,+2,+3,+4... ext
b. 1/16, 1/32 . multiplied by 1/2
c. 81, 234 multiplied by 3
d. -2, -7 subtract one more than the previous number subtracted
e. 53, 58 subtract 2, then add 5 to the next, then subtract again, then add again