A)
158 × 432 + 158 × 68 - 158 × 400 =
158 × ( 432 + 68 - 400 ) =
158 × ( 500 - 400 ) =
158 × 100 = 15800
B)
2300 × 28 - 28 × 2299 - 28 =
28 × ( 2300 - 2299 ) - 28 =
28 × 1 - 28 =
28 - 28 = 0
C)
1245 × 200 + 100 × 1245 - 1245 - 290 =
1245 × ( 200 + 100 ) - 1245 - 290 =
1245 × 300 - 1245 - 290 =
373500 - 1245 - 290 =
372255 - 290 = 371965