To find the slope you need to take the rise/run, which means the change of y divided by the change of x. So -7.3-2.7 is the change of y and 1.3-(-4.7) is the change in x. So the slope is equal to -1.666. Then if you take the x and y for one set of points and put them into y = -1.666x + b and solve for b to give you the intercept. So -7.3 = (-1.666)(1.3) + b, therefore b = -5.1342. Now the equation is y = -1.666x + -5.1342
To find an inverse, switch the x and the y and solve for the new y. Yours switched is x = 3y. Now solving for y we divide both sides by 3 to get y = x/3
