Find the mistake

1-The company is looking for sufficient workers to be successful. Nothing really grammatically wrong with this.  Just sounds a bit clumsy.  Would be better if it said.  The company is looking for sufficient workers to ensure its success.  'Looking for' is very informal so in a formal situation you would say 'recruiting' so this might be what they are looking for here.

2-My sister qualified in modern languages and now works as an interpreter.

3-The first heart transplant was carried out a very long ago.

4-A very experienced heart surgeon will perform the procedure on my heart.

5-Professor Magdi Yacoub is by nature sociable.

find Find the mistake

1-The company is looking for sufficient workers to be successful. (Suggestion of Frances is good)
2-My sister qualified as in modern languages and now works as an interpreter.
3-The first heart transplant was carried out made very long ago.
4-A very experienced heart surgeon will perform the process procedure on my heart.
5-Professor Magdi Yacoub provided to is sociable by nature.
5-Professor Magdi Yacoub proved to be sociable.