Reorder the following equations in ascending order of steepness.
y = 15x + 5y = 0.15x - 1y = xy = x + 100

Equations don't have steepness.  "Steepness" is the slope of the line you get when you graph the equation.  If you always massage the equation into the form
[ y = (something times x) + something },
then the number that multiplies 'x' is the slope of the graph..

y = 15x + 5
The slope is 15.

y = 0.15x - 1
The slope is 0.15 .

y = x
The slope is 1.  ( y = 1x )

y = x + 100
The slope is 1.  ( y = 1x + 100 )