3

#!/bin/bash

if [[ $3 == "add" ]]
then
let "result = $1 + $2"
echo $result


else
if [[ $3 == "mul" ]]
then
let "result = $1 * $2"
echo $result

else
if [[ $3 == "sub" ]]
then
let "result = $1 - $2"
echo $result
fi
fi
fi