W B

---------

3 : 2

**---- 5 units**

+ 120

---------

2 : 3

**----- 5 parts**

---------

5 p --> 5 u + 120

1 p --> 1 u + 120/5 = 1 u + 24

2 p --> 2 u + 2 x 24 = 2 u + 48

3p --> 3u + 3 x 24 = 3 u + 72

3 u + ? --> 2 u + 48

2 u + (120 - ?) --> 3 u + 72

Both equations will end up with 1 u --> 48 -

Solution 1

-----------

W [][][][][][]

B [][][][][][][][][]

5 u --> 120

1u --> 120 /5 = 24

W: 6 u --> 6 x 24 = 144 white buttons.

Solution 2

------------

W [][][][][][][][]

B [][][][][][][][][][][][]

10 u --> 120

1u --> 120/10 = 12

W: 6 u --> 12 x 6 = 72 white buttons.

Solution 3

-----------

W [][][][][][][][][][][][][][]

B [][][][][][][][][][][][][][][][][][][][][]

15 u --> 120

1 u --> 120/15 = 8

W: 12 u --> 12 x 8 = 96 white buttons.

etc.......