from tkinter import Tk, Button, Entry, Text, END, StringVar

window=Tk()

def km_to_miles():
    miles=float(e1_value.get())*1.62
    t1.insert(END, miles)

b1 = Button(window, text="Execute", command=km_to_miles)
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()