function solve() {
    function clickEvent() {
        let textElement = this.parentNode.children[1];
        let text = textElement.innerText.toString();
        let number = text.match(/\d+/)[0];
        text = text.replace(number, (+number + 1).toString());
        textElement.innerHTML = text;
    }
    //add event to links
    let linkElements = document.querySelectorAll('#exercise a');

    for (let linkElement of linkElements){
        linkElement.addEventListener('click', clickEvent);
    }
}