Xiao Gang took money to buy a fountain pen. After buying 2 pens, there was still 1.8 yuan left. If he bought 4 pens of the same pen, the difference was 2.4 yuan. How much money did Xiao Gang bring?
小刚带钱去买钢笔，买2枝后还剩1.8元，若买同样的笔4枝还差2.4元，小刚带了多少元钱．
<gadget id="calculator">1.8 + 2.4</gadget>
<output>4.2</output>

<gadget id="calculator">4 - 2</gadget>
<output>2</output>

<gadget id="calculator">4.2 / 2</gadget>
<output>2.1</output>

<gadget id="calculator">2.1 * 2</gadget>
<output>4.2</output>

<gadget id="calculator">4.2 + 1.8</gadget>
<output>6</output>

<result>6</result>