Let's roll up our sleeves and solve this. We have 64 and we're going to multiply it by 10, essentially adding 64 to itself 10 times.
Step 1: 0 + 64 = 64
Step 2: 64 + 64 = 128
Step 3: 128 + 64 = 192
Step 4: 192 + 64 = 256
Step 5: 256 + 64 = 320
Step 6: 320 + 64 = 384
Step 7: 384 + 64 = 448
Step 8: 448 + 64 = 512
Step 9: 512 + 64 = 576
Step 10: 576 + 64 = 640

So, 64*10 = 640