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
}
}