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In this post, I will solve/answer part (A), only.
Definition (see web-site https://www.torr.com/what-torr )
The torr (symbol: Torr) is a non-SI unit of pressure defined as 1/760 of an atmosphere.
It was named after Evangelista Torricelli, an Italian physicist and mathematician who discovered
the principle of the barometer in 1644.
Solution
0.978 atm = 0.978*760 = 743.28 torr.
Probably, you herd somewhen, that 1 atm = 960 mm of the mercury column.
So, 1 torr is the pressure corresponding to 1 (one) millimeter of the mercury column.
Therefore, to say that the air pressure is 743.28 torr is the SAME as to say
that the air pressure is 743.28 mm of the mercury column.
Solved, answered and explained in full.
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