OK, let's work through this together. We're starting with 155 and we're going to multiply it by 4, which means we add 155 to itself 4 times.
Step 1: 0 + 155 = 155
Step 2: 155 + 155 = 310
Step 3: 310 + 155 = 465
Step 4: 465 + 155 = 620

So, 155*4 = 620