Alright, let's solve this math problem step by step. First, we have the number 245. Next, we see the multiplication sign, which means we need to multiply something. And what are we multiplying it by? We multiply it by 21. So, we're going to take the number 245 and add it to itself 21 times.
Step 1: 0 + 245 = 245
Step 2: 245 + 245 = 490
Step 3: 490 + 245 = 735
Step 4: 735 + 245 = 980
Step 5: 980 + 245 = 1225
Step 6: 1225 + 245 = 1470
Step 7: 1470 + 245 = 1715
Step 8: 1715 + 245 = 1960
Step 9: 1960 + 245 = 2205
Step 10: 2205 + 245 = 2450
Step 11: 2450 + 245 = 2695
Step 12: 2695 + 245 = 2940
Step 13: 2940 + 245 = 3185
Step 14: 3185 + 245 = 3430
Step 15: 3430 + 245 = 3675
Step 16: 3675 + 245 = 3920
Step 17: 3920 + 245 = 4165
Step 18: 4165 + 245 = 4410
Step 19: 4410 + 245 = 4655
Step 20: 4655 + 245 = 4900
Step 21: 4900 + 245 = 5145

So, 245*21 = 5145