Solve this Time and Work question: Arjun can build a boundary wall alone in 9 hours and Danish can build the same wall alone in 10 hours. When they work together, coordination delays reduce their combined output by 10 bricks per hour. Even then, they finish the wall in 5 hours. How many bricks are used in the wall?

The verified answer to “Solve this Time and Work question: Arjun can build a boundary wall alone in 9 hours and Danish can build the same wall alone in 10 hours. When they work together, coordination delays reduce their combined output by 10 bricks per hour. Even then, they finish the wall in 5 hours. How many bricks are used in the wall?” is 900 bricks, option C. The question-specific working supplied with the item states: Let the wall contain N bricks. Arjun's hourly output = N/9 and Danish's hourly output = N/10. Their theoretical combined output is N/9 + N/10 = 19N/90 bricks per hour. They complete the wall in 5 hours, so actual output is N/5 = 18N/90. This gives N/90 = 10 and hence N = 900 bricks. This working identifies the relevant work-rate equation and connects the given information to the required result. After applying the verified rule, the required value or position is 900 bricks. The alternatives 720 bricks, 810 bricks and 990 bricks fail because each breaks at least one stated condition, transition, direction or arithmetic step. A plausible-looking option is not sufficient unless it reproduces the complete work-rate equation. This full replay leads only to 900 bricks, so option C is uniquely correct.