$#Dino$
`B=5/(2.1)+4/(1.11)+3/(11.2)+1/(2.15)+13/(15.4)`
`B/7=5/(1.2.7)+4/(1.7.11)+3/(11.7.2)+1/(7.2.15)+13/(15.7.4)`
`B/7=5/(2.7)+4/(7.11)+3/(11.14)+1/(14.15)+13/(15.28)`
`B/7=7/(2.7)-2/(2.7)+11/(7.11)-7/(711)+14/(11.14)-11/(11.14)+15/(14.15)-14/(14.15)+28/(15.28)-15/(15.28)`
`B/7=1/2-1/7+1/7-1/11+...+1/15-1/28`
`B/7=1/2-1/28`
`B/7=13/28`
`B=13/28:7=13/4`