,
39:26.
The second question, πD/πd=2.
So the diameter of the small circle is half that of the big circle, which is 4 cm.
The third question, football+basketball =20, football/basketball =7:3, which shows that football has 14 and basketball has 6. Suppose X footballs are bought later, then two footballs have the solution of (14+X): 20 = 4: 5.