Explanation

88 + 43 = 131

13+3=16 by skipping next 1 odd digit that is 5 we will add 7 to 16 16+7=23 by skipping next 2 odd digit to seven we will add 13 to 23 23+13=36 by skipping next 3 odd digit to 13 (i.e 15,17,19) we will ad 21 to 36 36+21=57 by skipping next 4 odd digit to 21 (i.e 23,25,27,29) we will ad 31 to 57 57+31=88 by skipping next 5 odd digit to 31 (i.e 33,35,37,39,41) we will ad 43 to 88 88+43=131`