Question 984023
I can't solve it, but I can rewrite it (solving means an equation)

distribute -3rt*2t^2 - 3rt(3r)
-6rt^3 - 9 r^2t

When multiplying, first figure out the sign, then multiply constants, then variables, do each separately and then combing.  That is where the - 6 came from, then r, then t*t^2