Ответ:

а)

\(40 : 5 = 8\).

\(84 \cdot 703 = 59\,052\), \(72\,640 : 8 = 9\,080\), \(3009 \cdot 240 = 722\,160\).

\(59\,052 - 312 + 9\,080 + 722\,160 = 799\,980\).

Ответ: 799 980.

б)

\(423 + 168 = 591\).

\(2980 \cdot 591 = 1\,761\,180\).

\(57 \cdot 17 - 209 = 969 - 209 = 760\).

\(760 \cdot 6 : 3 = 1\,520\), \(533\,700 : 9 = 59\,300\).

\(1\,761\,180 - 1\,520 + 59\,300 = 1\,818\,960\).

Ответ: 1 818 960.