You might be thinking of "distribution" or "distributive property"
Example:
2(3x+5) = 2*3x+2*5 = 6x+10
I multiplied the outer 2 by each term inside (3x and 5)
The table on the far left
You can tell because every time the x value increases by 1, the y value increases by exactly 1/2 every time
Ok, so you have your equation, 5·x+5-(5x+25).
First, do the prathases, so you have, 5x+5-5x-25.(5·x also means 5x)
Now, you need to combine like terms, and through that the xs cancel out, so you are left with -20 as you answer.
Amy's current age is 16 years greater than Peter's age, so Amy's current age is equal to x + 16.
6 years ago, Amy's age was equal to twice that of Peter's age at that point, so her age was 2(x - 6).
As currently her age is x + 16 then 6 years ago her age was x + 16 - 6, which is x + 10.
As 6 years ago her age was equal to 2(x - 6) and x + 10, we can see that x + 10 = 2(x - 6).
