Stan makes a playlist for the next time he goes running. He has 10 3-minute songs and 15 2-minute songs on his playlist. His entire run takes 100 minutes. If Stan wants a playlist to cover his entire run, how many more minutes of songs will he need in his playlist?
His playlist currently has a playtime of 10 songs * 3 minutes = 
<gadget id="calculator">10*3</gadget>
<output>30</output>
30 minutes from 3-minute songs.
It also has a playtime of 15 songs * 2 minutes = 
<gadget id="calculator">15*2</gadget>
<output>30</output>
30 minutes from 2-minute songs.
So far, his playlist lasts for 30 + 30 = 
<gadget id="calculator">30+30</gadget>
<output>60</output>
60 minutes.
He therefore still needs 100 minutes for his run - 60 minutes current playtime = 
<gadget id="calculator">100-60</gadget>
<output>40</output>
40 minutes.

<result>40</result>