What is the slope of this line?

A line is increasing if it goes up from left to right. The slope is positive, i.e. m > 0 {\displaystyle m>0} .

A line is decreasing if it goes down from left to right. The slope is negative, i.e. m < 0 {\displaystyle m<0} .

If a line is horizontal the slope is zero. This is a constant function.

If a line is vertical the slope is undefined (see below).

wholesale price is the initial price before markup. retail price comes after the markup.

a price of 8 bucks that's marked up by 100%   is

formula: initial price + (percent markup in fraction/decimal)(initial price)

8+(1)(8)

8+8

16

retail price is $16.