The wattage rating of an appliance W varies jointly as the square of the current I & the resistance R. If the wattage is 48 watts when the current is 0.4 ampere & the resistance is 300 ohms, find the wattage when the current is 0.1 ampere & the resistance is 250 ohms.

The equation I have so far is: W=k x square root of IR

Is that right?