Convert 23/4 to a mixed number

How many 4s can go into 23?

4, 8, 12, 16, 20..

That's the maximum that we can add without going over, with 3 left over, and we keep the same denominator, so 5 3/4

area of part 1:

a1=base*height/2=(8+2)*(8-2-2-1)/2=10*3/2=15 ft^2

area of part 2:

a2=length*width=(8+2)*1=10 ft2

area of part 3:

a3=length*width=8*2=16 ft2

total shaded area : a1+a2+a3=41 ft2

total area of the reactangle : a=16*8=128 ft2

total area of the nonshaded region : 128-41=87 ft2