`A = 1/(4.7) + 1/(7.10) + 1/(10.13) + ... + 1/(37.40)`
`3A = 3 . (1/(4.7) + 1/(7.10) + 1/(10.13) + ... + 1/(37.40))`
`3A = 3/(4.7) + 3/(7.10) + 3/(10.13) + ... + 3/(37.40)`
`3A = 1/4 - 1/7 + 1/7 - 1/10 + 10 - 1/13 + ... + 1/37 - 1/40`
`3A = 1/4 - 1/40`
`3A = 9/40`
`A = 9/40 : 3`
`A = 3/40`