Answer:
520 out of 800 students ride the bus
Step-by-step explanation:
Given


Required
Determine the number of students 
To do this, we simply multiply the proportion by the total number of students.
i.e.


Express the percentage as decimal


<em />
The absolute value
returns the "positive version" of a number.
In other words, if the number is positive, it remains positive; if the number is negative, it changes sign.
So, if we want
, we want the "positive version" of x to be 9.
This can happen in two ways: if x is already 9, then its absolute value is still nine. If instead x=-9, its positive value will be 9 again.
In formula, we have

because

The slope is the factor in front of x, so slope is 9.
The y intercept is 7 (that's the point of cross the y axis, where x=0)
There are multiple definitions of "standard form" for lines, so here are the two i can think of:
9x - y = -7 (the implicit function form)
or
y-7 = 9*(x-0) (the point-slope form)
Lmk if you have questions.