80 percent of 90 is the same as 40 percent of what number?

    80% of 90 may be found by multiply 90 by 0.8. Once you have that number, you can use it to set up a proportion with 2/5 (the simplified form of 40/100). Thus, you will write out 72/x = 2/5, since x is the number that you're solving for. Multiply numerators and denominators of opposite fractions to get the equation 72(5) = 2x. Finally, simplify 360 = 2x by dividing both sides by 2 to isolate the variable. You should have your answer by now.

for finding the midpoint of any given 2 pair of points simply add the respective x coordinates with other x coordinate and the y coordinate with other y coordinate and divide them by 2

in your question it will be :

(3+1)/2 for the x coordinate of mid point i.e 2

[8+(-4)]/2 for the y coordinate of midpoint i.e 2

so coordinates of mid point of points (3,8) and (1,-4) will be (2,2)

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