Write Script, using case statement to perform basic math operation such as addition subtraction multiplication division

#!/bin/bash
#

if test $# = 3
then
 case $2 in
  +) let z=$1+$3;;
  -) let z=$1-$3;;
  /) let z=$1/$3;;
  x|X) let z=$1*$3;;
  *) echo Warning - $2 invalied operator, only +,-,x,/ operator allowed
     exit;;
 esac
 echo Answer is $z
else
 echo "Usage - $0   value1  operator value2"
 echo "        Where, value1 and value2 are numeric values"
 echo "               operator can be +,-,/,x (For Multiplication)"
fi