Explanation: (D) Rahat এবং Mominul একত্রে 1 মিনিটে করে \(1/20\) অংশ কাজ। অর্থাৎ Rahat একা 1 মিনিটে করে \((1/20 - 1/30) = 1/60\) অংশ কাজ। অতএব সম্পূর্ণ কাজ করতে 60 মিনিট। (Note: The provided explanation has an error: it calculates Mominul's work rate by subtracting Rahat's from the combined rate, but the text states Rahat alone takes 30 mins, and together they take 20 mins. The calculation in the explanation is for Mominul's time, not Rahat's, and the final answer is correct for Mominul: \((1/20 - 1/30) = 3/60 - 2/60 = 1/60\). So Mominul takes 60 mins.)
