Answer:
Your age(a) is 15 in this case.
If your brother is 1/3 of your age, that means multiply your brother's age by 3
Your sister is 9, and is 4 years older than your brother. In that case, we now know that your brother is 5
With that information, we can put this into a valid equation.
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<em>turn 1/3 into a flipped fraction, 3/1 which is equal to 3</em>
<em>your brother's age is 5, so the first value would be 5</em>
<em>5 times 3 is 15, so that means a is 15</em>