3 and 4

3:

#include <iostream>
#include <thread>

int main() {
    std::cout << std:: thread::hardware_concurrency() << "\n";
    return 0;
}


4:
#include <iostream>
#include <thread>

void addSeven(long x, long* result) {
    *result = x + 7;
}

void addTwoNumbers(long x, long y, long* sum) {
    *sum = x + y;
}

void addThreeNumbers(long x, long y, long z, long* sum) {
    *sum = x + y + z;
}

int main() {
    long a = 10;
    long b = 15, c = 20;
    long x = 2, y = 5, z = 30;
    
    long result1, result2, result3;
    
    std::thread th1(addSeven, a, &result1);
    std::thread th2(addTwoNumbers, b, c, &result2);
    std::thread th3(addThreeNumbers, x, y, z, &result3);
    
    th1.join();
    th2.join();
    th3.join();
    
    std::cout << result1 << " " << result2 << " " << result3 << "\n";
    
    return 0;
}