An object moves at a constant rate. the graph shows the object's height at different times.
which equation represents the situation?
a.
y = −15x + 900
b.
y = −15x − 900
c.
y = 15x − 900
d.
y = 15x + 900

With linear graphs, there's two things you need to find, the y intercept and the slope. The y intercept is literally where the line touches the y axis. Looking at the graph you can see that it's at 900, so your number by itself has to be +900. The slope then is found by seeing how much y changes for every change in x. So you have two points, (20,600) and (40,300) which tell you that the line moves down 300 when it moves across 20. Your slope is then -300/20 which is -15. This goes in front of your x and you get your equation. SO your answer would be 

A. y = −15x + 900

Hope I helped:P