OK, let's work through this together. We're starting with 78 and we're going to multiply it by 5, which means we add 78 to itself 5 times.
Step 1: 0 + 78 = 78
Step 2: 78 + 78 = 156
Step 3: 156 + 78 = 234
Step 4: 234 + 78 = 312
Step 5: 312 + 78 = 390

So, 78*5 = 390