Answer is 40km
Explanation:
So in this question we can use a proportion
Since
28km is 70% we can write it equal to 70%
28=70
and since 100% is unknown we can write it equal to x
100=x
Then we put it in proportion form
28/x=70/100
Then cross multiply and divide
28(100)/70=x
Which would equal 40
The equation (form) is: 
The solution of the equation is: 
Explanation:
First, let's call the number we are going to solve for "x".
Then two thirds of this number can be written as:

Then "plus 4" means add 4 we get:

"is 7" means that the above expression is equal to 7 (as follows):

The solution of the above equation is:

C represents the number of four-packs of cartridges because the question says there are 4 pack of 42 ounceink cartridges that sell for 85.99...If you were ever to create an equation with this it would be 42c = 85.99
And you can plug in 4, 8, or 16 for c and check how much they would cost over all...your welcome, have a great day
diameter of human hair is around 0.0025cm
in scientific notation it is: 2.5x10^-3