from tkinter import *

window = Tk()

def km_to_miles():
    miles = float(e1_value.get())*1.6
    t1.insert(END,miles)

b1=Button(window,text = "Excute", command = km_to_miles)
#b1.pack() one way to set the position of button
b1.grid(row = 0, column = 0  )

e1_value = StringVar()
e1 = Entry(window, textvariable = e1_value)
e1.grid(row = 0, column = 1)

t1 = Text(window,height = 1, width = 20)
t1.grid(row = 0, column = 2)

window.mainloop()