PHP Multiply String服务中的值

I'm trying to multiply a value (sales tax) that is being returned from a service. I'm able to 'add' it without any problems, but I'm not able to get it to multiply using my string:

floatval(($service->PRICE)+floatval($service->SALES_TAX)+floatval($service->TRAVEL))

I've tried using:

floatval(($service->PRICE)*floatval($service->SALES_TAX)+floatval($service->TRAVEL))

and also

floatval(($service->PRICE*$service->SALES_TAX)+floatval($service->TRAVEL))

But both only return the Travel amount, instead of the Price * Sales Tax + Travel.

Any help is greatly appreciated!