69 426 -435:[363:3-(b×2+6×4)]+12345:5=71 890.Afla-l pe b

69 426 - 435 : [ 363 : 3 - ( b x 2 + 6 x 4 ) ] + 12 345 : 5 = 71 890

69 426 - 435 : [ 121 - ( b x 2 + 24 ) ] + 2469 = 71 890

69 426 - 435 : [ 121 - ( b x 2 + 24 ) ] = 71 890 - 2469

69 426 - 435 : [ 121 - ( b x 2 + 24 ) ] = 69 421

435 : [ 121 - ( b x 2 + 24 ) ] = 69 426 - 69 421 = 5

121 - ( b x 2 + 24 ) = 435 : 5 = 87

b x 2 + 24 = 121 - 87

b x 2 = 34 - 24

b x 2 = 10

b = 10 : 2

b = 5