Prime number is only divisible by 1 and itself. ... No other whole numbers can multiply together to make 11. 15 is not a prime number because the factors of 15 are 1, 3, 5 and15 ( ). 15 has more than 2 factors, so it is not a prime number.

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