a, $A = 1/1.7 + 1/7.13 + 1/13.19 +1/19.25 + 1/25.31 + 1/31.37 $
$ A= 1- 1/7 + 1/7-1/13 +1/13 -1/19+1/19-1/25+1/25-1/31+1/31-1/37 $
$ A= 1- 1/37 = 36/37 $
b , $ B/7 = 5/2.7 +4/7.11 +3/11.14 + 1/14.15 + 13/15.28 $
$ B/7 = 1/2 - 1/7 + 1/7-1/11+1/11-1/14+1/14-1/15 +1/15 -1/28 $
$ B/7 = 1/2 -1/28 = 13/28 $
⇒ $ B= 13/4 $