First multiply the parenthesis:
20 - b = 1/3b + 16/3
Then combine like terms:
20 -b + b = 1/3b + b + 16/3
20 - 16/3 = 1/3b + b + 16/3 -16/3
20 - 16/3 = 1/3b + b
44/3 = 4/3b
and if your looking for b;
44/3 (divided by) 4/3 = b
11 = b...is your final answer!
hope it helped :)