First, distribute the numbers outside of the parenthesis like how the blue arrows show (Multiply the outside number to each term)
8r+(4t-10r)+(12t+8r)
8r+4t-10r+12t+8r
Then, combine like terms. (Add/subtract the numbers with the same variable (t or r)).
Combing t terms:
8r+4t-10r+12t+8r
8r-10r+8r+16t
Combing r terms:
6r+16t
^This is our final answer because we can no longer simplify it.