Simplified evaluation: When a=0.6, b=1.2, find the value of 7a-2a+3b.
化简求值：当a=0.6，b=1.2时，求7a-2a+3b的值．
<gadget id="calculator">5 * 0.6</gadget>
<output>3</output>

<gadget id="calculator">3 * 1.2</gadget>
<output>3.6</output>

<gadget id="calculator">3 + 3.6</gadget>
<output>6.6</output>

<result>6.6</result>