Ответ:

from tkinter import *

def calculate():

 a = float(entry_a.get())

 b = float(entry_b.get())

 c = float(entry_c.get())

 result = a + b + c

 label_result.config(text="Результат: " + str(result))

root = Tk()

root.title("Калькулятор")

label_a = Label(root, text="a=")

label_a.pack()

entry_a = Entry(root)

entry_a.pack()

label_b = Label(root, text="b=")

label_b.pack()

entry_b = Entry(root)

entry_b.pack()

label_c = Label(root, text="c=")

label_c.pack()

entry_c = Entry(root)

entry_c.pack()

button_calc = Button(root, text="Показать Результат", command=calculate)

button_calc.pack()

label_result = Label(root, text="")

label_result.pack()

root.mainloop()

Объяснение: