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Step-by-step explanation:

Scale factor  = 1 : 7

a)Let the length of the house in the scale drawing = x

1:7 :: x : 21

Product of means = Product of extremes

 7*x = 1* 21

     x =

     x = 3

Length of the house in the scale drawing = 3 in

b) Height of the real house =y

1 : 7 :: 4 : y

Product of extremes = product of means

1 * y = 7*4

   y = 7*4

   y = 28

Height of real house = 28 feet

f(x) has value 150 at x= 0

and 0 at x= 3

so d(f(x))/dt = slope = -150/3 = -50

25% is the answer