Sorry but u should write ur expression so i can solve it....
Answer:
if you want to know the temperature it's 78
Step-by-step explanation:
84-6 is 78
You could estimate by doing 600x3=1800
(becasuse of the 0's in 600 it is easier to do 6*3=18 and then add two 0's to the end 1800)
then you simply multiple 640x3=1920