（Ⅰ）求数列 $\left\{a_n\right\}$ 的通项公式；

（Ⅱ）设 $\left\{\frac{b_n}{a_n}\right\}$ 的首项为1，公比为 $3$ 的等比数列，求数列 $\left\{b_n\right\}$ 的前 $n$ 项和为 $T_n$ ．

    I'll tell you a secret. There's a place that gets me every time: whenever I'm there. I can't help but cry. Where is it? It's thousands of metres high in the sky, in a plane, especially when there's a heart-warming comedy on.

    Why am I admitting (承认) this now? Because I'm not alone. The British singer Ed Sheeran says he gets emotional (情绪激动的) when flying too. Also a survey carried out by Gatwick Airport in London found that 15％ of men admit they're more likely (可能的) to cry during films in planes than watching at home. And 41％ of men admit they often try to hide their tears in another survey by Virgin Atlantic (a British airline). In all, 55％ of air travellers in the Virgin Atlantic study said they get emotional when flying. So, what's going on? A study from the Netherlands has shown that adults cry because of feelings of separation, loneliness or powerlessness. All of these are easily experienced when flying: you're far from family, often alone, and have no control over the flight.

    Another   ▲   is that when you're in a plane in the sky, there's not a lot you can do. So you are able to pay more attention to the movies you watch. Then there's the physical space. In a plane, air pressure and oxygen levels are lower, and this can affect (影响) our brain and emotions. On a flight, you may be leaving loved ones or really wanting to see them again, or you might have had a drink at a time you usually wouldn't, and if you see a scene that reflects your emotional state, without doubt it's easier for you to cry.