If 3 is added to a number and the sum is tripled , the result is 21 more than the number. find the number.

If 3 is added to the number: x + 3

b) ... and the sum is tripled ...

"The sum" is "x + 3" so: 3 (x+3)

c) ... the result is 27 more than the number.

27 more than the number is x + 27

d) Put it all together:

3 (x + 3) = x + 27

Solve for x:

1) Distribute the left side of the equation:

3x + 9 = x + 27

2) Subtract x from each side of the equation:

2x + 9 = 27

3) Subtract 9 from each side of the equation:

2x = 18

4) Solve for x:

x = 9

Check:

1) x = 9

2) 3 (x + 3) = x + 27

3) 3 ([9] + 3) = [9] + 27

4) 3 (12) = 9 + 27

5) 36 = 36

So, therefore The answer is correct