<div id="counter">
<input type="button" id="buttonCountPlus" value="+">
<div id="buttonCountNumber">1</div>
<input type="button" id="buttonCountMinus" value="-">
</div>

<div id="calculation">150</div>

#counter {
  display: flex;
  justify-content: space-between;
  width: 80px;
}

let calculate = document.getElementById("calculation");
let count = document.getElementById("buttonCountNumber");
calculation = document.getElementById("calculation").innerHTML;

document.getElementById("buttonCountPlus").onclick = function() {
  let countPlus = count.innerHTML;
  if(+countPlus <= 3){
    count.innerHTML++;
    let countPlus = count.innerHTML;
    calculate.innerHTML = calculations(countPlus) ;
  }
}

document.getElementById("buttonCountMinus").onclick = function() {
  let countMinus = count.innerHTML;
  if(+countMinus >= 2){
    count.innerHTML--;
    let countMinus = count.innerHTML;
    calculate.innerHTML = calculations(countMinus) ;
  }
}

calculations = (count) => {
  return calculation+` * ${count} = ` + (+count)*(+calculation);
}