Creating 6 boxes with numbers in ruby prawn

boxes.rb

require "prawn"

Prawn::Document.generate("boxes.pdf") do
  y = 20
  x = 700
  a = 15
  gap = 5

  6.times do |number|
    stroke_rectangle [y, x], a, a
    draw_text "#{number}", :size => 10, :at => [y + gap,x - (2*gap)]
    y += gap + a
  end

end