7 * 8 = 56
9 * 4 = 36
7 * 36 = 252
252 + 56 = 308
100 * 308 = 30800

7 - 4 = 3
7 * 9 = 63
63 - 8 = 55
3 + 55 = 58
100 - 58 = 42

4 + 7 = 11
8 + 100 = 108
7 * 11 = 77
9 * 77 = 693
108 + 693 = 801