how to change font size

[menator01]

import tkinter as tk

root = tk.Tk()
root['padx'] = 8
root['pady'] = 4
tk.Label(root, text='Button with font and a size of10').pack()
btn = tk.Button(root, text='Button 1', font=('tahoma 10'))
btn.pack()

tk.Label(root, text='Button with font and size of 40', font=('verdana 20')).pack()
btn2 = tk.Button(root, text='Button 2', font=('verdana 40'))
btn2.pack()

tk.Label(root, text='Button with font and size of 20 and bold', font=('times 20 bold')).pack()
btn3 = tk.Button(root, text='Button 3', font=('times 20 bold'))
btn3.pack()
root.mainloop()