A store has sold 90 notebooks, which is 20% of all the notebooks they had. How many notebooks did the store have at first?​

In the diagram, points d and e are marked by drawing arcs of equal size centered at b such that the arcs intersect ba and bc. then, intersecting arcs of equal size are drawn centered at points d and e. point p is located at the intersection of these arcs. based on this construction, m , and m