The base of a cone is something circular, like a circle or an ellipse.
The rest of the options (square, triangle, and pentagon) are all based of pyramids, not cones. Cones have to have a circular base because otherwise they'd be pyramids.
The answer is the first choice: 7, 15, 20.
When you want to know what three numbers can make up a triangle. All you have to do is take the first two numbers and add them up. If the sum is larger than the third number, it can form a triangle. If the sum of the first two numbers are smaller than the third number, it cannot form a triangle.
Hope this helped
Prime factors are factors of a number that are, themselves, prime numbers. There are many methods to find the prime factors of a number, but one of the most common is to use a prime factor tree.
