What is the formula for determining a PERT weighted average?

Question $35$ options:

$($optimistic time $+4$ x most like time $+$ pessimistic time$)/6$

$($optimistic time $+6$ x most like time $+$ pessimistic time$)/4$

$($optimistic time $+4$ x most like time $+$ pessimistic time$)/4$

$($optimistic time $+6$ x most like time $+$ pessimistic time$)/6$