Answer:
y = 3x + 12
Explanation:
so the point slope form of an equation is is y minus y1 = M (x - X1) where why one equals the first point Y value and X1 is the first point x value and M equals the slope . if you substitute your question into this equation you will you will get y - 21 = 3 ( x - 3).
if you want to be fancy haha you can put this into the linear equation form y = mx + b so then you can add 21 to the other side to get y=3(x-3)+21. after that you foil and get y equals 3x - 9 + 21 . simplify and you get why equals 3x + 12