June has $500 for buying school supplies for the new school year. She buys four maths books at $20 each, six more science books than maths books at $10 each, and twice as many art books as maths books at $20 each. If she also bought music books, how much money did she spend on music books?
The total cost of maths books is 4*20 = $
<gadget id="calculator">4*20</gadget>
<output>80</output>
80$.
She bought six more science books than maths books which totals 6+4 = 
<gadget id="calculator">6+4</gadget>
<output>10</output>
10 books.
If each science book cost her $10 she spent 10*10 = $
<gadget id="calculator">10*10</gadget>
<output>100</output>
100 on science books.
There were twice as many art books as maths books which total 2*4 = 
<gadget id="calculator">2*4</gadget>
<output>8</output>
8.
The total cost for art books is 8*20 = $
<gadget id="calculator">8*20</gadget>
<output>160</output>
160.
The total amount that she used for maths, science, and art books is 160+100+80 = $
<gadget id="calculator">160+100+80</gadget>
<output>340</output>
340.
The amount she spent on music books is 500 - 340 = $
<gadget id="calculator">500-340</gadget>
<output>160</output>
160.

<result>160</result>