Triangles ABC and DFE are similar, since angles A and D are congruent; B and F are congruent; and it follows that C and E are also congruent, since the sum of the interior angles of any triangles is 180°.
Sides AC and DE correspond to each other. Since DE is 4 times as long as AC, triangle DFE is 4 times larger than ABC.
DF corresponds to AB. DF is 4 times as long as AB, so it has length 4*4 = 16.
