Как-то так:

1. Задание

a = int(input("Enter the value of a: "))

b = int(input("Enter the value of b: "))

if (a >= 0 and b >= 0) or (a < 0 and b < 0):

   print("YES")

else:

   print("NO")

2. Задание

num = int(input("Enter a four-digit number: "))

if num < 1000 or num > 9999:

   print("Invalid number")

else:

   tens_digit = num // 10 % 10

   if tens_digit % 2 == 1:

       print("YES")

   else:

       print("NO")

3. Задание

A = int(input("Enter the cost of the book in UAH: "))

B = int(input("Enter the cost of the book in COP: "))

C = int(input("Enter the amount Tanya has in UAH: "))

D = int(input("Enter the amount Tanya has in COP: "))

book_cost = A * 100 + B

tanya_money = C * 100 + D

if tanya_money >= book_cost:

   print("YES")

else:

   print("NO")