#### Answer

y=3x-12

#### Work Step by Step

If we know the slope m of an equation and a point (a, b) that is on the graph of the equation, then we can determine the equation of the line using point-slope form:
y-b=m(x-a)
Since we're given that the line has a slope of 3 and that the point (7, 9) lies on the graph, we can plug these numbers in and determine the equation of the line in point-slope form. Therefore, the equation would be
y-9=3(x-7)
We can then solve for y by first applying the distributive property to the right side of the equation and rewriting it as
y-9=3x-21
Then, to solve for y, we'll add 9 to both sides of the equation
y=3x-12