Answer:
The width of the aside should be set to 33.33%
Explanation:
Given:
Let F1 = Fixed width of an aside element in a fixed layout
F1 = 300 pixels
Let F2 = Fixed width of its parent element (body)
F2 = 900 pixels
Let W = The width, after converting the page from fixed to fluid layout
W is calculated as F1/F2
W = F1/F2
W = 300 pixels/900 pixels
W = 300/900
W = 0.3333 ---- Convert to percentage
W = 33.33%
Hence, the width of the aside should be set to 33.33%