ANSWER
60 buttons.
EXPLANATION
Let the number of buttons in the container be x.
Then the number of buttons that are black are:
[tex] \frac{7}{10} x[/tex]
The number of buttons that are white
[tex] \frac{3}{10} x[/tex]
The difference between the white and the black buttons
[tex] \frac{4x}{10} = 24[/tex]
Solve for x.
[tex]4x = 240[/tex]
[tex]x = \frac{240}{4} [/tex]
[tex]x = 60[/tex]
Hence there are 60 buttons in the container.