Translate to an equation p $25 potted plants and s $20 shrubs total $300,graph the equation and use the graph to determine three different combination of potted plants and shrubs that total $300?

25p + 20s = 300

Easiest way to find ordered pairs is to look at the intercepts.
Here they would be (0,15) and (12,0)

the slope of the line is -25/20 = -5/4

that is, for every decrease of 5 the 'ss, there will be an increase of 4 in the p's

so take any point, decrease the s by 5, increase the p by 4
from (0,15) --> (4,10) --> (8,5) --> (12,0)

Your graph should confirm that.
The above 4 points are the only ones containing positive integers, fractions or negatives would not make any physical sense.