Answer:
Part a)
![a = 3.97 m/s^2](https://img.qammunity.org/2020/formulas/physics/high-school/rhk7upd67qmwe8w2s9zruo7e9d1jhvukrq.png)
Part b)
![T = 1255.4 N](https://img.qammunity.org/2020/formulas/physics/high-school/zfkj4i8v4bj6xp64mpx3raxq8orlqm1hze.png)
Step-by-step explanation:
Part a)
By force equation at position of Robinhood we will have
![T - mg = ma](https://img.qammunity.org/2020/formulas/physics/high-school/h1gz2i5rl8hrf03dr03tg76zcryb17x4sz.png)
on the other side of the rope we will have
![Mg - T = Ma](https://img.qammunity.org/2020/formulas/physics/high-school/57ij1aae17z8ruxhrd8n05o8ezfakojgzm.png)
now by above two equations we have
![Mg - mg = (M + m) a](https://img.qammunity.org/2020/formulas/physics/high-school/pknwe7ejrtzvlftry3cf3vdrlykramnx8v.png)
![a = (M - m)/(M + m) g](https://img.qammunity.org/2020/formulas/physics/high-school/gp9jmdwcug3e5a6luqq77ecw64urpqrhbo.png)
plug in all data in the equation we will have
![a = (215 - 91.1)/(215 + 91.1)(9.81)](https://img.qammunity.org/2020/formulas/physics/high-school/at4p5fa97awnrhpirokgbgjqhdbp3loste.png)
![a = 3.97 m/s^2](https://img.qammunity.org/2020/formulas/physics/high-school/rhk7upd67qmwe8w2s9zruo7e9d1jhvukrq.png)
Part b)
From above equation we have
![T - mg = ma](https://img.qammunity.org/2020/formulas/physics/high-school/h1gz2i5rl8hrf03dr03tg76zcryb17x4sz.png)
![T = mg + ma](https://img.qammunity.org/2020/formulas/physics/high-school/p88xtpbrqq532czo1eaxvbn5b60upvyuxw.png)
![T = 91.1(9.81 + 3.97)](https://img.qammunity.org/2020/formulas/physics/high-school/klzgtaimtjxj8rabwv0girc6pxf0zcpnxp.png)
![T = 1255.4 N](https://img.qammunity.org/2020/formulas/physics/high-school/zfkj4i8v4bj6xp64mpx3raxq8orlqm1hze.png)