một mảnh vườn hình chữ nhật có chiều dài hơn chiều rộng 10m nếu tăng chiều dài thêm 6m giảm chiều rộng đi 3m thì diện tích khu rừng tăng 12 m vuông tính diện tích khu vườn ban đầu

To solve this problem, we can start by setting up the equation for the area of the original garden. Let's denote the original length of the garden as L (in meters) and the original width as W (in meters). We are given that the length is 10m longer than the width, so we have: $$ The area of a rectangle is given by the formula: $$ So, the area of the original garden can be expressed as: $$ Substituting $$ into this equation gives us: $$ Now, we are told that if we increase the length by 6m and decrease the width by 3m, then the area increases by 12 square meters. This gives us another equation: $$ We can simplify this equation to get: $$ Expanding this equation gives us: $$ $$ $$ Now, we need to find out the value of A when W=20. Substituting W=20 into our expression for A gives us: $$ Therefore, the area of the original garden is $$