등차수열의 특정한 항만 더하기

using System;

public class Solution {
    public int solution(int a, int d, bool[] included) {
        int answer = 0;
        for(int i = 0; i<included.Length;i++)
        {
            if(included[i])
            {
                answer += (a + i * d);
            }
        }
        return answer;
    }
}