How do you score a word that has multiple bonuses?
Note that this is something that is impossible to pull off in a standard game as the only row/column that has both a triple word and a double word is the one with the starting space and you need 8 tiles to get from the double word space to the triple word space.

According to the Scrabble rules you would take the value of the word and multiply by by 6, and then add 50 points. (The rules don't explicitly state this due to it being impossible, but they do account for 2 doubles or 2 triples so there is no reason to think that a triple and a double would work differently)