Ahair dryer with a resistance of 9.6 ohms operates at 120 volts for 2.5 minutes. the total electrical energy used by the dryer during this time interval is
(1)2.9 × 103j
(2)3.8 × 103j
(3)1.7 × 105j
(4)2.3 × 105j

For the answer to the question above,
hm's law : u=ri , and : energy=uiδt 
then : i=u/r (we don't have , the current) ; then : energy=e=u²δt/r 
u is voltage in volts (v), δt is the time of plugging in hours (h) , r is resistance in ohms (ω) 
we have 30 days in seconds : δt =10 min per day * 30 days =1/6 hour per day * 30 days =5 hours 
u=120 v; r=9.6 ω 
then : e=120²*5/9.6 = 7500 wh =7.5 kwh

Milliseconds. . . . . .