A battery stores 1.8×105 J of energy and powers an electric motor whose power output behaves as follows: the motor delivers a constant 2.0 kW for the first t seconds, after which its power decreases linearly to zero over the next 10 s. If the battery is completely discharged by this operation, what is the value of t?
a) 90 s
b) 85 s
c) 75 s
d) 95 s