3 times the sum of 6 and a number is 33

Step-by-step explanation:

Let the number in question be 'n'. Then twice the sum of the number and 3 is written as:

2 (n + 3)

Three times the difference of the number and 9 is written as:

3 (n - 9)

The problem says these two are equal, so:

2 (n + 3) = 3 (n - 9)

2n + 6 = 3n - 27

Add 27 to both sides:

2n + 33 = 3n

Subtract 2n from both sides:

33 = n (the number is 33)