What is the scale factor of 10cm=5m?

First lets work out the length of the top side which joins the points (-1,7) and (-5,5):-

this =  sqrt ( (7-5)^2 + (-1 - (-5)^2 )

=  sqrt (4 + 16)

= sqrt 20

Now find length of the longer side which is distance between the points (-1,7) and (4, -3)

this is sqrt ( (-1 - 4)^2 +  (7 - -3)^2)

= sqrt  125

Area of the rectangle = sqrt 20 * sqrt 125

= sqrt 2500

= 50 units^2  Answer