This problem is based on Rate and Work.
Formula used will be Rate * Time = Work Done

Let Rate of Bob be B and Rate of Jack be J

Working at a constant rate, Bob can produce \(\frac{x}{3 }\) widgets in 8 minutes
=> B * 8 = \(\frac{x}{3 }\)
=> B = \(\frac{x}{{3*8} }\) = \(\frac{x}{24 }\)

Quantity A = The number of minutes it will take Bob to produce \(5x\) widgets
=> B * T = 5x
=> \(\frac{x}{24 }\) * T = 5x
=> T = \(\frac{{5x * 24}}{x }\) = 120 mins

Working at a constant rate, Jack can produce \(2x \) widgets in 40 minutes
=> J * 40 = 2x
=> J = \(\frac{2x}{40 }\) = \(\frac{x}{20 }\)

Quantity B = The number of minutes it will take Jack to produce \(6x \) widgets
=> J * Time = 6x
=> \(\frac{x}{20 }\) * Time = 6x
=> Time = \(\frac{{6x*20}}{x}\) = 120 mins

=> Clearly, Quantity A = Quantity B = 120 mins

So, Answer will be C
Hope it helps!

Watch the following video to learn How to Solve Work Rate Problems