Here's the solution ~
As we know, we can calculate the circumference of a circle in terms of its diameter as :
where, c = circumference and d = diameter
And also, circumference of circle is terms of radius (r) is :
Now, let's move on to questions ~
<h3>First </h3>・ ．━━━━━━━†━━━━━━━━━．・
<h3>Second</h3><h3 /><h3 /><h3 /><h3>・ ．━━━━━━━†━━━━━━━━━．・
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<h3>Fifth </h3>・ ．━━━━━━━†━━━━━━━━━．・
<h3>Sixth</h3>➖➖➖➖➖➖➖➖➖➖➖➖➖➖➖➖➖