cannot apply java lang integer android

1val a = result.text.toString()
2 val b = resultHist1.text.toString()
3
4 if(!a.isNullOrEmpty() &&  !b.isNullOrEmpty() ){
5    val a = a.toInt()
6    val b = b.toInt()
7    calcHist1.text = (a+b).toString()
8   }
9   else
10   {
11   calcHist1.text = ""
12   }