The speed of a boat in still water is 11 km/h. It can go 12 km upstream and return downstream to original point in 2 hours 45 minutes. Find the speed of the stream.

A man spent ₹2800 on buying a number of plants priced at ₹x each. Because of the number involved, the supplier reduced the price of each plant by one rupee. The man finally paid ₹2730 and received 10 more plants . Find x.

The total expenses of a trip for certain number of people is ₹ 18,000. If three more people join them, then the share of each reduces by ₹ 3,000. Take x to be the original number of people, form a quadratic equation in x and solve it to find the value of x.

A car travels a distance of 72 km at a certain average speed of x km per hour and then travels a distance of 81 km at an average speed of 6 km per hour more than its original average speed. If it takes 3 hours to complete the total journey then form a quadratic equation and solve it to find its original average speed.