Series of odd numbers are obtained by adding 2 to an odd number to get its consecutive odd number. In the first row, the odd numbers are obtained as follows: 13,13+2=15,15+2=17,17+2=19 b=15 and c=17 In the second row, the odd numbers are obtained as follows: 7,7+2=9,9+2=11 a=11 13+b+c+19=13+15+17+19=64