we are given to simplify

Open the bracket and write the like terms together

when the bases are same then the exponents gets added

If you would tell me the whole problem I could answer it
1. Given (12+3)x, we can sum the numbers in the parenthesis to get 15x
2. Given 12x+3x, we can factor x to get (12+3)x and get the same as 1.
3. Given (12+3x)x, we have to distribute the x and we have 
4. This expression is already simplified.
Answer: x=35
Step-by-step explanation: hi! i’m happy to help. subtract the three from both sides, multiply the entire problem by 5 to even out the x, and there’s your answer :)