$\dfrac{2}{35}$`+`$\dfrac{2}{63}$`+`$\dfrac{2}{99}$`+`$\dfrac{2}{143}$`+`$\frac{2}{195}$`+`$\dfrac{2}{255}$
`=2/5.7 + 2/7.9 + 2/9.11 + 2/11.13 + 2/13.15 + 2/15.17`
`= 1/5 - 1/7 + 1/7 - 1/9 + 1/9 - 1/11 + 1/11 - 1/13 + 1/13 - 1/15 + 1/15 - 1/17`
`= 1/5 - 1/17`
`= 17/85 - 5/85 = 12/85`