in used car lot, there are three times as many red cars as green cars. If tommorow 12 green cars are sold and 3 red cars are added,then there will be 6 times as many red cars as green cars. How many green cars are currently in the lot?

I cant grasp why "there are three times as many red cars as green cars" translates to r=3g . I keep translating it to 3g=r but i dont see why i am wrong? also how does 3+r=6(g-12) translate from "if 12 green cars are sold and 3 red cars are added, there will be 6 times as many green ones"..

any help? also where could I go for translation tutorial?