A box has a total surface area of 100. The length of the box is equal to twice its width, as well as equal to 3 less than its height. What is the height of the box?

h=7

Step-by-step explanation:

First we need to define the formula for surface area

2(wl+hl+hw)=100

Now we can replace length with x

That makes width .5x and height x+3

2(.5x^2+x^2+3x+.5x^2+1.5x)=100

2(2x^2+4.5x)=100

2x^2+4.5x=50

2x^2+4.5x-50=0

Insert into quadratic equation (a=2x^2, b=4.5, c=-50)

x=4 or -6.25

x can't be negative so x is 4

h=x+3=7

h=7

a 4/6 = 9/12   not proportional

step-by-step explanation:

to find which are not proportional, we can use cross products

if it is true, they are proportional.   if it is not true, they are not proportional.

a 4/6 = 9/12

4* 12 = 6*9

48 = 54

not this is not proportional  

b 2/3 = 12/18  

2* 18 = 3 * 12

36 = 36

this is proportional

c 5/4 = 10/8  

5*8 = 4*10

40 = 40

this is proportional

d 7/5 = 35/25

7*25 = 5 * 35

175 = 175

is proportional