So we have to find the equation that relates the dollars in Priya's saving account and the number of weeks passed after she started saving. For the amount of money we can use M and for the weeks we can use W. By looking at the picture you can notice that the graph of the function is a straight line. This means that the function we are looking for is a linear function which means that its equation can be written like this:
Where m and b are parameters that we have to find. The solutions to this equation are the points in the graph which have the form (W,M). So basically, if we take two points from the graph we can use them to construct two equations and with those equations we can find m and b and solve part d.
So let's pick two points. If you look carefully at the graph you'll notice that the line passes through the points (0,80) and (5,200). Then we can build two equations: one with W=0 and M=80 and another one with W=5 and M=200. Then we get:
From the first equation we get 80=b. We can use this value in the second equation replacing b with 80:
And then we substract 80 from both sides:
And we divide both sides by 5:
So m=24 and the equation looks like this:
Then if W is the number of weeks of saving and M are the dollars in savings account the equation we are looking for is M=24W+80.