Question 277106
3{[4 (n-4)+19]-[3(4n-2)+5]} 
The { are the same as ( ) and [ ].  They're used in pairs to section off parts of the expression.
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To simplify these, work from the inside out.
Look for parentheses, brackets, etc, that you can eliminate.
3{[4(n-4)+19]-[3(4n-2)+5]}
On the left, 4(n-4) can be dealt with, and 3(4n-2) on the right side.
= 3{[4n-16+19]-[12n-6+5]}
Then combine terms, the numbers in this case.
= 3{[4n+3] - [12n-1]}
Then apply the -1 (minus sign) to [12n-1]
= 3{[4n+3 - 12n+1]}
Combine terms again
= 3{[-8n+4]}
That's the same as 3[-8n+4]
Then the 3:
= -24n + 12