16
Arithmetic
They are: 17+12 = 29 and 17-12 = 5
Tony is 12! because if his brother is 17 there would be 5 years difference between their agaes and 12+17=29!
The sequence interval is 2 4 6 8 ( this is the difference of number). so the missing number is -1 if I'm not mistaken.
29
16
Arithmetic
They are: 17+12 = 29 and 17-12 = 5
The Least Common Multiple of 29 and 17 is 493.
The GCF of 17 and 29 is 1.1
21
The pattern of odd numbers
5, 11, 17, 23, 29
-29.
The GCF is 1.
t(n) = 12*n + 5