Well...5x12 = 60, and the factors of 60 are 1,2,3,4,5,6,10,12,15,20,30 and 60...so I'm thinking only 3x30, 4x15, 5x12 and 6x10? (As all numbers have to be => 3 to fit the shapes in.)
Well it would be 3x20 (not 3x30) but even so not all those rectangle dimensions are possible to form.