To simplify this calculation, check the last digit of the sum. Since all values end in 0, the sum of the tens digit is:
Green Tea tens $= 80$, Coffee tens $= 10$, Black Tea tens $= 90$.
\( 80 + 10 + 90 = 180 \) (ends in 80).
Looking at the options, only (C) ends in 80, which helps you identify the correct answer quickly.