OK, let's work through this together. We're starting with 90 and we're going to multiply it by 8, which means we add 90 to itself 8 times.
Step 1: 0 + 90 = 90
Step 2: 90 + 90 = 180
Step 3: 180 + 90 = 270
Step 4: 270 + 90 = 360
Step 5: 360 + 90 = 450
Step 6: 450 + 90 = 540
Step 7: 540 + 90 = 630
Step 8: 630 + 90 = 720

So, 90*8 = 720