OK, let's crack this. We're given 870 and our task is to multiply it by 7. Essentially, we'll be adding 870 to itself 7 times.
Step 1: 0 + 870 = 870
Step 2: 870 + 870 = 1740
Step 3: 1740 + 870 = 2610
Step 4: 2610 + 870 = 3480
Step 5: 3480 + 870 = 4350
Step 6: 4350 + 870 = 5220
Step 7: 5220 + 870 = 6090

So, 870*7 = 6090