I’m honestly having the biggest brain fart with this right now, end of the school year brain , someone

 sin θ = opposite/hypotenuse      &          tan θ = opposite/adjacent
sin 30 = 18/y                                          tan 30 = 18/x
       y = 18/sin 30                                           x = 18/tan 30
       y = 36                                                     x ≈ 31.2

you can also use the 30° - 60° - 90° shortcuts
side opposite 30 = a, side opposite 60 = a√3, side opposite 90 = 2a
then, 18 = a
          x = a√3= 18√3
          y = 2a  = 2(18) = 36

127 millimeters is the answer