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.
Let u = 5x+1. Then du = 5·dx, and your integral is

Answer: 18 and 36
Step-by-step explanation:
The least common multiple is the smallest which is 18.
Answer:
x=1/4 , y=-1/4. You can confirm this by substituting the numbers in.
Step-by-step explanation: