Alright, let's solve this math problem step by step. First, we have the number 780. Next, we see the multiplication sign, which means we need to multiply something. And what are we multiplying it by? We multiply it by 5. So, we're going to take the number 780 and add it to itself 5 times.
Step 1: 0 + 780 = 780
Step 2: 780 + 780 = 1560
Step 3: 1560 + 780 = 2340
Step 4: 2340 + 780 = 3120
Step 5: 3120 + 780 = 3900

So, 780*5 = 3900