$解：? (1)?∵點(diǎn)?D?為?AB?的中點(diǎn)$
$∴?BD= AD= 30m?$
$∵?FM//CG?$
$∴?∠BDF=∠BAC= 30° ?$
$?BF=sin 30°×BD=15m?$
$?FD= cos 30°×BD= 15\sqrt{3}m?$
$若?∠BEF=45°，??EF=BF= 15m?$
$∴當(dāng)?∠BEF≤45°，??EF≥15m?$
$∴?DE≤11.0m?$
$?(2)?過(guò)點(diǎn)?D?作?DP⊥CG，?垂足為點(diǎn)?P?$
$∵?∠DAC=30°?$
$∴?DP=sin 30°×AD=15m，?$
$?AP= cos 30°×AD =15\sqrt{3}m?$
$?DM=AP+AG=(15\sqrt{3}+27)m?$
$∵?∠HDM=30°?$
$∴?HM=tan 30°×DM≈30.6m?$
$∴?HG= HM+ MG=45.6m?$
