Answer:
Option A. [tex]40\ cm[/tex]
Step-by-step explanation:
we know that
The lateral area of a cone is equal to
[tex]LA=\pi rl[/tex]
we have
[tex]LA=400\pi \ cm^{2}[/tex]
[tex]r=10\ cm[/tex]
substitute and solve for l (slant height)
[tex]400\pi=\pi (10)l[/tex]
simplify
[tex]400=(10)l[/tex]
[tex]l=400/10=40\ cm[/tex]