After years of decline in his health, Tim has now realised that smoking is unhealthy. Until now, he has regularly smoked 120 cigarettes each week. To help him quit, he is determined to reduce this amount by 5 cigarettes every week from now on.
(1) Explain why the number of cigarettes Tim smokes each week will form an arithmetic sequence with u1=115. State the common difference for the sequence.
(2) How many weeks will it take before Tim has smoked his last cigarette?
(3) Find the total number of cigarettes Tim will smoke before he successfully quits.