In order to determine the scale factor, calculate the quotient between the area of the two trapezoids.
Consider that the area of the trapezoid is given by the sum of the area of a rectangle ans a triangle.
For the bigger trapezoid you have:
A1 = (4)(4) + (6-4)(4)/2
A1 = 16 + (2)(4)/2
A1 = 16 + 4
A1 = 20
For the smaller trapezoid:
A2 = (1)(1) + (1.6 - 1)(1)/2
A2 = 1 + 0.3
A2 = 1.3
Finally, the scale factor is:
A1/A2 = 20/1.3 = 15.38