∴DM=4cm,NM=3cm，
∵EN⊥AD，
∴MN= =3，
It can be seen from the properties of folding and parallel lines that ∠END=∠NDC=∠NDE,
∴EN=ED, let EM=x, then ED=EN=x+3,
ED2=EM2+DM2 comes from Pythagorean theorem, that is, (x+3)2=x2+42.
The solution is x=0, that is, em = 7/6 cm.