OK, no figure, but from the comment is sounds like the grey area is the big circle minus the small circle.
The diameter of the small circle is 2 so its radius is 1 and its area πr² is π.
The radius of the larger circle is 4, so area 16π
The shaded area is 16π - π
Answer: 15π
4 and 7 and 8 and 9 and10
Answer: a=10
Step-by-step explanation: