It takes joan 6 times longer than jane to file the reports. together, they can file the reports in 30 minutes. how long would it take each woman to file the reports by herself?

Jane = 35 minutes 
Joan = 210 minutes or 3 hours and 30 minutes

You have to consider the job done = 100% or 1 (100& =1)
let t₁ be the time spent by Joan to complete the 100% of the job AND
let t₂ be the time spent by Jane to complete the 100% of the job
We know that t₁=6t₂ (given),then Joan need 6t₂ to complete the 100% of the job

In 1Minute Joan completes 1/6t₂  (part of the job). In 30 min she competes 30/6t₂ OR 5/t₂
In 1 MINUTE Jane completes 1/t₂ (part of the job).In 30 min she competes 30/t₂
But we know that 5/t₂ +30/t₂ = 1 (100% of the Job)
Reduce same denominator (5/t₂ +30/t₂) = 1/t₂
& t₂ = 35 min needed by Jane to complete the 100% of the job alone &
35 x 6 =210 min (or 3hr & 30 min) needed by Joane to complete the 100% of the job alone

Hello!
volume of sphere =4/3.pi.r^3