Sara invested $3,400 six years ago. Today, her investment is worth $4,200. Which formula will correctly compute her rate of return?

i = ($4,200/$3,400)6 -1

i = ($4,200/$3,400)1/6 - 1

i = [($4,200/$3,400) - 1]1/6

i= ($3,400/$4,200)1/6