Brainlist asap !! _

1) find the simple interest: _
principal: $6000
interest rate: 5%
time: 6 months

_
2) find the interest rate: _
principal: $500
interest: $60
time: 3 years

_

3) find the principal amount: _
interest rate: 4%
interest: $784
time: 20 years

also if you guys have the time can you please explain how to do problems like these it'll mean alot !!