Đáp án:

 4) \(\left\{ \begin{array}{l}
y = 16\\
z = 18\\
z = 15
\end{array} \right.\)

Giải thích các bước giải:

\(\begin{array}{l}
2)\left\{ \begin{array}{l}
x = \dfrac{2}{3}y\\
z = \dfrac{7}{5}y\\
\dfrac{2}{3}y - y + \dfrac{7}{5}y = 32
\end{array} \right.\\
 \to \left\{ \begin{array}{l}
x = \dfrac{2}{3}y\\
z = \dfrac{5}{3}y\\
\dfrac{{16}}{{15}}y = 32
\end{array} \right.\\
 \to \left\{ \begin{array}{l}
x = \dfrac{2}{3}y\\
z = \dfrac{5}{3}y\\
y = 30
\end{array} \right.\\
 \to \left\{ \begin{array}{l}
x = 20\\
z = 50\\
y = 24
\end{array} \right.\\
3)\left\{ \begin{array}{l}
x = \dfrac{3}{4}y\\
z = \dfrac{5}{3}y\\
2.\dfrac{3}{4}y - 3y + \dfrac{5}{3}y = 6
\end{array} \right.\\
 \to \left\{ \begin{array}{l}
x = \dfrac{3}{4}y\\
z = \dfrac{5}{3}y\\
\dfrac{1}{6}y = 6
\end{array} \right.\\
 \to \left\{ \begin{array}{l}
x = \dfrac{3}{4}y\\
z = \dfrac{5}{3}y\\
y = 36
\end{array} \right.\\
 \to \left\{ \begin{array}{l}
x = 27\\
z = 60\\
y = 36
\end{array} \right.\\
4)\left\{ \begin{array}{l}
x = \left( {\dfrac{3}{4}:\dfrac{2}{3}} \right)y\\
z = \left( {\dfrac{3}{4}:\dfrac{4}{5}} \right)y\\
x + y + z = 49
\end{array} \right.\\
 \to \left\{ \begin{array}{l}
x = \dfrac{9}{8}y\\
z = \dfrac{{15}}{{16}}y\\
\dfrac{9}{8}y + y + \dfrac{{15}}{{16}}y = 49
\end{array} \right.\\
 \to \left\{ \begin{array}{l}
\dfrac{{49}}{{16}}y = 49\\
x = \dfrac{9}{8}y\\
z = \dfrac{{15}}{{16}}y
\end{array} \right.\\
 \to \left\{ \begin{array}{l}
y = 16\\
z = 18\\
z = 15
\end{array} \right.\\
5)\left\{ \begin{array}{l}
3x - 3 = 2y - 2z\\
4y - 4z = 3z - 9\\
2z + 3y - 2 = 50
\end{array} \right.\\
 \to \left\{ \begin{array}{l}
4y - 7z =  - 9\\
3y + 2z = 52\\
3x - 3 = 2y - 2z
\end{array} \right.\\
 \to \left\{ \begin{array}{l}
y = \dfrac{{346}}{{29}}\\
z = \dfrac{{235}}{{29}}\\
x = \dfrac{{103}}{{29}}
\end{array} \right.\\
6)\left\{ \begin{array}{l}
x = \dfrac{2}{3}y\\
z = \dfrac{5}{3}y\\
\dfrac{2}{3}y.y.\dfrac{5}{3}y = 80
\end{array} \right.\\
 \to \left\{ \begin{array}{l}
\dfrac{{10}}{9}{y^3} = 80\\
x = \dfrac{2}{3}y\\
z = \dfrac{5}{3}y
\end{array} \right.\\
 \to \left\{ \begin{array}{l}
{y^3} = 72\\
x = \dfrac{2}{3}y\\
z = \dfrac{5}{3}y
\end{array} \right.\\
 \to \left\{ \begin{array}{l}
y = \sqrt[3]{{72}}\\
x = \dfrac{{2.\sqrt[3]{{72}}}}{3}\\
z = \dfrac{{5.\sqrt[3]{{72}}}}{3}
\end{array} \right.
\end{array}\)