\[\boxed{\mathbf{4}.}\]
\[1)\ 5a^{3}b - 3ab^{2} + 4ab^{2} -\]
\[- a^{3}b = - 2a^{3}b + ab^{2}\]
\[2)\ 2xy^{2}x^{3} - 3xyxy +\]
\[+ 8x^{2}y^{2}x^{2} - 14 = 8x^{4}y^{2} +\]
\[+ 2x^{4}y^{2} - 3x^{2}y^{2} - 14 =\]
\[= 10x^{4}y^{2} - 3x^{2}y^{2} - 14\]
\[3)\ 1\frac{1}{3}\text{ab}\left( - 6a^{2}b \right) -\]
\[- 0,7a^{3} \cdot 20b - b^{2} \cdot 7a^{3} =\]
\[= - \frac{4}{3} \cdot 6a^{3}b^{2} - 14a^{3}b -\]
\[- 7a^{3}b^{2} =\]
\[= - 8a^{3}b^{2} - 7a^{3}b^{2} - 14a^{3}b =\]
\[= - 15a^{3}b^{2} - 14a^{3}b\]