The figures are similar, so the corresponding sides form a ratio of 3/2 AB corresponds to EF (AB is the first two letters of ABCD; EF is the first two letters of EFGH)
Set up the following equation and isolate EF through cross multiplying AB/EF = 3/2 18/EF = 3/2 18*2 = EF*3 36 = 3*EF 3*EF = 36 3*EF/3 = 36/3 EF = 12
