When the the time period becomes so long that according to the demand it is possible to adjust the production, it is a long-term condition. Since the time duration is quite long, we can change all the variable and fixed factors, and changing the fixed and variable factors can help adjust, both the supply as well as demand.
In the given figure, the initial demand curve of firm is DD. Whereas SQ is very short period supply curve. SPS is short period supply curve and LPS is long period supply curve. The initial equilibrium point is E0. It is determined by the interaction of SQ (Supply Curve) and DD (demand curve). In this stage, OP is the price and OQ is the quantity. In the long run, equilibrium is at E2, where new demand curve D1D1 intersect LPS at E2. Therefore, new price is OP1 and new quantity is OQ1.
