In need of help.

I am making a simple annuity calculator and I am having trouble converting the annuity equation so it can be used in AS3.

I have spent the last hour and a half or so trying to convert this equation and I feel like an idiot. FVoa = PMT [((1 + i)ⁿ - 1) / i]

Here is my code below

var investment:Number
var interest:Number
var time:Number
var total:Number

button_btn.addEventListener(MouseEvent.CLICK, calculate)
function calculate(event:MouseEvent):void
{
    investment=Number(investment_txt.text)
    interest=Number(interest_txt.text)/100
    time=Number(time_txt.text)
    total=investment*(Math.pow(((1 + interest/12), time-1)/interest/12))
    total_txt.text=String(total)
}

And here is my stage if you want to see it.

When I try and run my program I get this error. "1084: Syntax error: expecting rightbrace before rightparen."

Edit: Added a missing parenthesis now I get this error "1136: Incorrect number of arguments.  Expected 2."