The sum of 9 and three times a number is 21. what is the number?
equation:

n =

To solve equations like this we need to do inverse operations.

First we need to build an equation: 9+3x=21

We pass the nine to the other side, subtracting the 9 to 21, that leaves us with 3x=12

After that we just divide 12 by 3, wich gives us x=4, or, as it says in the question: n=4

Now let's double check:

N=4, since 3*4=12 and 12+9=21

Hope it is helpful :)

Best answer that i found on yahoo ok   set :   x= length of 2nd piece in cm  x- 3= length of 1st piece in cm  x-4= length of 3rd piece in cm  then since you know they all came from the 20 cm ribbon you add them together and set them equal to 20x+ x-3 +x-4 = 20  3x - 7= 20  3x= 27  x= 9  the shortest piece is the third piece which is x- 4  x-4  9-4 = 5  the length of the smallest piece is 5 cm.  the other lengths are  9 cm  6 cm

The correct awnser is 29.76 pounds.