document.getElementById("btn").addEventListener("click", calculate)
let costEl = document.getElementById("cost-el")
form.addEventListener("input")

function calculate() {
    
    let foodEl = document.getElementById("food-select").value
    let transportEl = document.getElementById("transport-select").value
    let baloonEl = document.getElementById("balloon-checkbox").value
    
    
    if ((foodEl === "" ) || (transportEl === "")){ 
        costEl.textContent = "Please, select two options below :)"
    }else if((foodEl != "" ) && (transportEl != "")){
        foodEl = parseInt(foodEl)
        transportEl = parseInt(transportEl)
        costEl.textContent = foodEl + transportEl
    }
     
    
    
}