TypeError: "Unsupported operand types: string * float"

I have the Error: TypeError Unsupported operand types: string * float
The Error is in this Line:
$pricere1 = $db_price * $validate->getIntervalFactor($runtime) * $mainrabatt_script;
I tried to find the Error but nothing worked for me :/

>Solution :

So you are multiplying string with float. One of your variable is holding string value.
You can var_dump() to see which variable hold the string data, and change the value to float. Otherwise you can cast those variable to float.

$pricere1 = (float)$db_price * (float)$validate->getIntervalFactor($runtime) * (float)$mainrabatt_script;