OK, let's work through this together. We're starting with 648 and we're going to multiply it by 7, which means we add 648 to itself 7 times.
Step 1: 0 + 648 = 648
Step 2: 648 + 648 = 1296
Step 3: 1296 + 648 = 1944
Step 4: 1944 + 648 = 2592
Step 5: 2592 + 648 = 3240
Step 6: 3240 + 648 = 3888
Step 7: 3888 + 648 = 4536

So, 648*7 = 4536