1400÷( 12+5+3)=70

Wang Xiaoming: 70× 12=840.

Zhang Xiaodong: 70×5=350.

Zhang Xiao: 70×3=2 10 (yuan)

the second question

70cm = 0.7m

1577 ÷ (0.7× 3.14×100) ≈ 7.17 (minutes)

Please adopt it. Thank you.