elasticity of income if price changes by 10 percent
Try work it out step by step and don't just concentrate on the math.

Suppose Arista has income of $w$, and the price of whatzits is $p$. She spends 10% of that on whatzits, so how many whatzits does she buy? Let's call this $q$.

Now suppose income is now $x \cdot w$ (so if her income increases by 3% then $x$ is 1.03.) The price of whatzits is still the same, $p$. How many whatzits does she buy now? Let's call this $q'$.

The income elasticity of [quantity] demand[ed] is simply the percentage change in quantity demanded divided by the percentage change in income:

$$e = \frac{\frac{q' - q}{q}}{\frac{xw - w}{w}}.$$