Draw the black-and-white chequered flag used at the finish of a Formula 1 race.

Draw a rectangle with 9 columns and 7 rows of squares. Each square is 30 steps wide and 30 steps high. The squares touch, with no gaps.

The top-left square is black. Alternate black and white squares across each row. The first square in each new row has the opposite color from the row above it.

Start each row at x = -135. The bottom edge of the top row is at y = 75. Move down 30 steps for each next row. Use penup() and goto() to move between squares without drawing lines.

Write a function named draw_square(color) that draws one filled square. Then write a function named draw_row(y, first_color) that draws nine alternating squares on one row. Use your functions to draw all seven rows.