Graphical solution to the "Shop Puzzle"

See Puzzle A Day, "A Shop Puzzle", from March 8, 2025.

This demonstrates how to solve this puzzle using a graphical approach. Substitute C = (100 - A - B) into each constraint to express each constraint only in terms of A and B. Plot lines representing the three constraints on a unit grid. Any solutions must reside within the triangular area bounded by the three constraint lines. Inspection shows there is only one whole-number solution within the triangular area, namely A = 55, B = 26, (and therefore C = 19). This is the only solution to the puzzle.