You Own Two Fast-Food Restaurants $R _ { 1 } = 323 + 11.8 t,$

You own two fast-food restaurants. During the years 2000 to 2008, the sales for the first restaurant have been increasing according to the function $R _ { 1 } = 323 + 11.8 t,$ $t = 0,1,2,3,4,5,6,7,8$ where $R _ { 1 }$ represents the sales (in thousands of dollars) and $t$ represents the year, with $t = 0$ corresponding to 2000. During the same nine-year period, the sales for the second restaurant have been decreasing according to the function $R _ { 2 } = 470 - 18.6 t,$ $t = 0,1,2,3,4,5,6,7,8.$ Write a function that represents the total sales for the two restaurants to determine whether the total sales have been increasing or decreasing.

A) $R _ { T } = - 147 - 6.8 t,$ total sales have been decreasing.
B) $R _ { T } = 793 + 68 t,$ total sales have been increasing.
C) $R _ { T } = 793 - 6.8 t,$ total sales have been decreasing.
D) $R _ { T } = - 147 + 30.4 t,$ total sales have been increasing.
E) $R _ { T } = 147 - 30.4 t,$ total sales have been decreasing.