The sum of numbers or expression involves adding the expressions and the numbers together.
Assume that the sum of the degrees is given as:

The above sum can be rewritten as:

Take the sum of all the numbers (including -2 in bracket)

If the sum of the degrees is given as
, then the number of years he worked would be 6
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Answer:
b is ya answer hope you have a blessed day
Step-by-step explanation:
Add the like terms.
12r+11r-4r= 19r
5s+9s=14s
-7t=-7t
19r+14s-7t