OK, let's work through this together. We're starting with 598 and we're going to multiply it by 15, which means we add 598 to itself 15 times.
Step 1: 0 + 598 = 598
Step 2: 598 + 598 = 1196
Step 3: 1196 + 598 = 1794
Step 4: 1794 + 598 = 2392
Step 5: 2392 + 598 = 2990
Step 6: 2990 + 598 = 3588
Step 7: 3588 + 598 = 4186
Step 8: 4186 + 598 = 4784
Step 9: 4784 + 598 = 5382
Step 10: 5382 + 598 = 5980
Step 11: 5980 + 598 = 6578
Step 12: 6578 + 598 = 7176
Step 13: 7176 + 598 = 7774
Step 14: 7774 + 598 = 8372
Step 15: 8372 + 598 = 8970

So, 598*15 = 8970