Sure thing, let's get straight to it. We start with 840 and we're going to multiply it by 5, which means adding 840 to itself 5 times.
Step 1: 0 + 840 = 840
Step 2: 840 + 840 = 1680
Step 3: 1680 + 840 = 2520
Step 4: 2520 + 840 = 3360
Step 5: 3360 + 840 = 4200

So, 840*5 = 4200