Mohan wants to buy a trapezium shaped field. Its side along the river is parallel to and twice the side along road. If the area of his field is 10500 m² and the perpendicular distance between the two parallel sides is 100 m, find the length of the side along the river.

Let the length of the side along the river = x m
∴      Other side (parallel to the road) = 
∴  Area of the trapezium shaped field = 
                                                            = 
                      But area of the field = 10500 m²
 ∴                              75x m² =  10500 m²
or                                    
       Thus, length of the side along the river = 140 m