OK, let's work through this together. We're starting with 891 and we're going to multiply it by 4, which means we add 891 to itself 4 times.
Step 1: 0 + 891 = 891
Step 2: 891 + 891 = 1782
Step 3: 1782 + 891 = 2673
Step 4: 2673 + 891 = 3564

So, 891*4 = 3564