Explanations and Answers:
Ok so to do this you just need to plug a bunch of different numbers into a bunch of different formulas :)
Diameter:
The diameter is the distance from one side of the circle to the other. In this case it is the given value: 15
Radius:
The radius is the distance from the center to any point on the edge of the circle. It is also half of the diameter. So, in this case you just have to take the diameter and divide it by 2.
15÷2=7.5
Circumference:
The circumference is the distance around the entire outside of the circle (essentially the perimeter). To find the circumference you multiply the diameter by π (Unless told otherwise use 3.14 as π).
15×π=?
15×3.14=47.1
Area:
To find the area of a circle you have to square your radius (multiply it by itself) and then multiply that by π.
πr²=?
π×7.5²=?
π×56.25=?
3.14×56.25=176.625
If you need any more help or further explanations just let me know!!