Final answer:
The font size of the child element is 64 pixels, which is calculated by multiplying the parent's font size of 32px by the child's font-size property of 2em.
Step-by-step explanation:
When calculating the font size of a child element based on its parent's font size using em units in CSS, we take the parent's font size and multiply it by the value set for the child's font-size property. In this example, the parent element has a font size of 32px and the child element has a font size of 2em.
To find the font size of the child element in pixels, we multiply 32 by 2 (the em value), which gives us:
64px.
Therefore, the child element's font size is 64 pixels.