ab7 + ab + 5ab = 699
100 a + 10 b + 7 + 10 a + b + 500 + 10 a + b = 699
120 a + 12 b = 699 - 507
12 ( 10 a + b ) = 192
10 a + b = 192 : 12
10 a + b = 16
ab = 16
ab7 + 16 + 516 = 699
ab7 = 699 - 532
ab7 = 167
verific: 167 + 16 + 516 = 699
