What is the product of 5 - 3i and 4 - 5i?

For this case we have the following complex numbers:
 5 - 3i
 4 - 5i
 Multiplying both numbers we have:
 (5 - 3i) * (4 - 5i)
 (5 * 4) + (5 * (- 5i)) + ((-3i) * 4) + ((-3i) * (- 5i))
 Rewriting we have:
 20 - 25i - 12i + 15i ^ 2
 20 - 37i + 15 (-1)
 20 - 37i - 15
 5 - 37i
 
 the product of 5 - 3i and 4 - 5i is:
 5 - 37i