John earned $18 on Saturday but he only managed to earn half that amount on Sunday. He earned $20 the previous weekend. How much more money does he need to earn to give him the $60 he needs to buy a new pogo stick?
John earnt $18 / 2 = $
<gadget id="calculator">18/2</gadget>
<output>9</output>
9 on Sunday.
In total, John made $18 + $9 + $20 = $
<gadget id="calculator">18+9+20</gadget>
<output>47</output>
47 over the two weekends.
John needs $60 - $47 = $
<gadget id="calculator">60-47</gadget>
<output>13</output>
13 extra to buy the pogo stick.

<result>13</result>