Preeti's rate is \(\frac{100}{75} =\frac{4}{3}\), while Mariska's rate is \(\frac{50}{30} =\frac{5}{3}\). This means that when they work together their rate becomes \(\frac{4}{3}+ \frac{5}{3} = \frac{9}{3}\).

Quantity A is computed taking into account that P and M together make 3 sandwich a minute, thus they make 180 sandwich in 60 minutes.

Quantity B: Mariska alone prepares 5 sandwich in 3 minutes, thus working 30 minutes she makes 50 sandwiches. When they work together they have 60 sandwiches left to do at a rate of 3 sandwiches a minute, thus it takes other 20 minutes to finish the sandwiches. 30 + 20 = 50 minutes.

Answer A