Two-thirds a numer plus 4 is 7

Since we don't know the number yet, we'll give it a name. 
That will make it easier to work with. 
It can have any name.  I've decided to call it ' Z '.

-- The number                                             Z

-- Two thirds of the number                    2/3 Z

-- Two thirds of the number plus 4         2/3 Z + 4

The question says that makes 7 :          2/3 Z + 4 = 7

Subtract  4  from each side:                   2/3 Z      = 3

Multiply each side by  3 :                        2  Z       = 9

Divide each side by  2 :                              Z       = 4.5