Without delay, let's solve this. We've got 780 and we will be multiplying it by 5, that is, adding 780 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