Side FG is proportional to side BC. When showing that two figures are similar, they should always be typed in the order of the points they correspond to. In this instance, ABCD ~ EFGH, meaning that AB ~ EF, BC ~ FG, CD ~ GH, and AD ~ EH. Let's use a simpler example, with similar triangles MNO and XYZ.
MNO ~ XYZ Since the two triangles are written in this specific order, each side should be similar to the side in the same order on the other triangle.
MN ~ XY
NO ~ YZ
MO ~ XZ
Hope this helps!