a is a natural number, what is the simplest fraction of ((3+a)/(9+3a))?
a是自然数，((3+a)/(9+3a))化成最简分数是多少．
<gadget id="calculator">1 / 3</gadget>
<output>1/3 = around 0.333333</output>

<result>1/3 = around 0.333333</result>