我试着在VBA中使用函数计算简单的利息金额，但它不起作用

Function CalculateInterest(principal As Double, rate As Double, time As Double) As Double
    CalculateInterest = principal * rate * time
End Function

Sub CalculateInterestAmount()
    Dim principal As Double
    Dim rate As Double
    Dim time As Double
    Dim interestAmount As Double
    
    principal = 1000 ' 设置本金为1000
    rate = 0.05 ' 设置利率为5%
    time = 2 ' 设置时间为2年
    
    interestAmount = CalculateInterest(principal, rate, time) ' 调用CalculateInterest函数计算利息金额
    
    MsgBox "利息金额为：" & interestAmount
End Sub