OK, let's crack this. We're given 390 and our task is to multiply it by 56. Essentially, we'll be adding 390 to itself 56 times.
Step 1: 0 + 390 = 390
Step 2: 390 + 390 = 780
Step 3: 780 + 390 = 1170
Step 4: 1170 + 390 = 1560
Step 5: 1560 + 390 = 1950
Step 6: 1950 + 390 = 2340
Step 7: 2340 + 390 = 2730
Step 8: 2730 + 390 = 3120
Step 9: 3120 + 390 = 3510
Step 10: 3510 + 390 = 3900
Step 11: 3900 + 390 = 4290
Step 12: 4290 + 390 = 4680
Step 13: 4680 + 390 = 5070
Step 14: 5070 + 390 = 5460
Step 15: 5460 + 390 = 5850
Step 16: 5850 + 390 = 6240
Step 17: 6240 + 390 = 6630
Step 18: 6630 + 390 = 7020
Step 19: 7020 + 390 = 7410
Step 20: 7410 + 390 = 7800
Step 21: 7800 + 390 = 8190
Step 22: 8190 + 390 = 8580
Step 23: 8580 + 390 = 8970
Step 24: 8970 + 390 = 9360
Step 25: 9360 + 390 = 9750
Step 26: 9750 + 390 = 10140
Step 27: 10140 + 390 = 10530
Step 28: 10530 + 390 = 10920
Step 29: 10920 + 390 = 11310
Step 30: 11310 + 390 = 11700
Step 31: 11700 + 390 = 12090
Step 32: 12090 + 390 = 12480
Step 33: 12480 + 390 = 12870
Step 34: 12870 + 390 = 13260
Step 35: 13260 + 390 = 13650
Step 36: 13650 + 390 = 14040
Step 37: 14040 + 390 = 14430
Step 38: 14430 + 390 = 14820
Step 39: 14820 + 390 = 15210
Step 40: 15210 + 390 = 15600
Step 41: 15600 + 390 = 15990
Step 42: 15990 + 390 = 16380
Step 43: 16380 + 390 = 16770
Step 44: 16770 + 390 = 17160
Step 45: 17160 + 390 = 17550
Step 46: 17550 + 390 = 17940
Step 47: 17940 + 390 = 18330
Step 48: 18330 + 390 = 18720
Step 49: 18720 + 390 = 19110
Step 50: 19110 + 390 = 19500
Step 51: 19500 + 390 = 19890
Step 52: 19890 + 390 = 20280
Step 53: 20280 + 390 = 20670
Step 54: 20670 + 390 = 21060
Step 55: 21060 + 390 = 21450
Step 56: 21450 + 390 = 21840

So, 390*56 = 21840