Xiao Ming's mother bought a bag of apples and pears. It is known that the number of apples is twice that of pears. They eat 5 apples and 4 pears every day. A few days later, the pears have been eaten, and there are still 15 apples left. How many apples did mom buy?
小明的妈妈买来一袋苹果和梨，已知苹果的只数是梨的2倍．他们每天吃去5只苹果、4只梨．几天以后，梨已吃完，还剩下15只苹果．妈妈买来苹果多少只？
<gadget id="calculator">4 * 2</gadget>
<output>8</output>

<gadget id="calculator">8 - 5</gadget>
<output>3</output>

<gadget id="calculator">15 / 3</gadget>
<output>5</output>

<gadget id="calculator">5 * 5</gadget>
<output>25</output>

<gadget id="calculator">25 + 15</gadget>
<output>40</output>

<result>40</result>