The below code requires knowledge of binary search.

#include<bits/stdc++.h>
using namespace std;

// Upper bound: The smallest index such that arr[ind]>N(Strictly greater than).
int upperBound(vector<int> arr, int key){  // Here key is the element we want to find upperbound for.
    int low=0,high=arr.size()-1,ans=arr.size();  
    while(low<high){
        int mid=(low+high)/2;
        if(arr[mid]>key) {
            ans=mid;
            high=mid-1;
        }
        else low=mid+1;
    }
    return ans;
}

int main(){
    vector<int> v = {5, 6, 7, 8, 9, 15, 17};
    int num=9;
    int s= upperBound(v,num);
    cout << "Number of elements greater than " << num << " is " << v.size()-s <<endl;
    return 0;
}

Hope this helps.

where did you submit ? Can you share the group link so I check the problem?