text: 
  function verificar(){
  
  let num = window.document.getElementById('txtnum')
  let tab = window.document.getElementById('seltab')
  
  let num1 = window.document.getElementById('txtnum1')
  let tab1 = window.document.getElementById('seltab1')
  
  let num2 = window.document.getElementById('txtnum2')
  let tab2 = window.document.getElementById('seltab2')
  
  let num3 = window.document.getElementById('txtnum3')
  let tab3 = window.document.getElementById('seltab3')
  
   if(num.value.length != 0){
          let numx = Number(num.value)
          let c = 1
          tab.innerHTML=''
          while( c <= 10){
              let item =  document.createElement('option') //Criando o elemeto de opções
              item.text = `${c} x ${numx} = ${c*numx}`//Parte de dentro do option
              item.value=`tab${c}` //identifica o valor da tabela selecionada dentro de cada valor option. exemplo 10x3 esta na tabeça tab3 do resultado
              tab.appendChild(item)
              c++
              document.getElementById('txtnum').value ="";
          }       
      }else if(num1.value.length != 0){
          let numz = Number(num1.value)
          let d = 1
          tab1.innerHTML=''
          while( d <= 10){
              let item1 =  document.createElement('option')
              item1.text = `${numz} / ${d} = ${numz/d}`
              item1.value=`tab${d}`
              tab1.appendChild(item1)
              d++
              document.getElementById('txtnum1').value ="";
          }       
          
      }else if(num2.value.length != 0){
          let numh = Number(num2.value)
          let e = 1
          tab2.innerHTML=''
          while( e <= 10){
              let item2 =  document.createElement('option')
              item2.text = `${e} + ${numh} = ${e+numh}`
              item2.value=`tab${e}`
              tab2.appendChild(item2)
              e++
              document.getElementById('txtnum2').value ="";
          }
      }else if(num3.value.length != 0){
          let numz = Number(num3.value)
          let f = 1
          tab3.innerHTML=''
          while( f <= 10){
              let item3 =  document.createElement('option')
              item3.text = `${numz} - ${f} = ${numz- f}`
              item3.value=`tab${d}`
              tab3.appendChild(item3)
              f++            
              document.getElementById('txtnum3').value ="";
          } 
  }else
      window.alert(`Informe um numero`)
  }
  
  /* function limpar(){
    item.innerHTML='';
    item1.innerHTML='';
    item2.innerHTML='';
    item3.innerHTML='';
  
  }  */
  