Alright, let's solve this math problem step by step. First, we have the number 258. Next, we see the multiplication sign, which means we need to multiply something. And what are we multiplying it by? We multiply it by 15. So, we're going to take the number 258 and add it to itself 15 times.
Step 1: 0 + 258 = 258
Step 2: 258 + 258 = 516
Step 3: 516 + 258 = 774
Step 4: 774 + 258 = 1032
Step 5: 1032 + 258 = 1290
Step 6: 1290 + 258 = 1548
Step 7: 1548 + 258 = 1806
Step 8: 1806 + 258 = 2064
Step 9: 2064 + 258 = 2322
Step 10: 2322 + 258 = 2580
Step 11: 2580 + 258 = 2838
Step 12: 2838 + 258 = 3096
Step 13: 3096 + 258 = 3354
Step 14: 3354 + 258 = 3612
Step 15: 3612 + 258 = 3870

So, 258*15 = 3870