You are required to create a simple calculator that returns the result of addition, subtraction, multiplication or division of two numbers.

Your function will accept three arguments:

The first and second argument should be numbers.

The third argument should represent a sign indicating the operation to perform on these two numbers.

if the variables are not numbers or the sign does not belong to the list above a message “unknown value” must be returned.

# Example:

```
calculator(1,2,"+"); //=> result will be 3
calculator(1,2,"&"); //=> result will be "unknown value"
calculator(1,"k","*"); //=> result will be "unknown value"
```

## Solution

```
function calculator(a,b,sign){
try {
return eval(`${a} ${sign} ${b}`)
} catch (e) {
return 'unknown value'
}
}
```