$\begin{equation*} \begin{cases} 4x + 15y = -42 | * 3 &\\ -6x + 25y = -32 | * 2 & \end{cases} \end{equation*}$
$\begin{equation*} \begin{cases} 12x + 45y = -126 &\\ -12x + 50y = -64 & \end{cases} \end{equation*}$
12x + 45y − 12x + 50y = −126 − 64
95y = −190
y = −190 : 95
y = −2
4x + 15y = −42
4x = −42 − 15y
4x = −42 − 15 * (−2)
4x = −42 + 30
4x = −12
x = −12 : 4
x = −3
Ответ: (−3;−2)

$\begin{equation*} \begin{cases} 9x + 8y = -53 | * 3 &\\ 15x + 12y = -27 | * (-2) & \end{cases} \end{equation*}$
$\begin{equation*} \begin{cases} 27x + 24y = -159 &\\ -30x - 24y = 54 & \end{cases} \end{equation*}$
27x + 24y − 30x − 24y = −159 + 54
−3x = −105
x = −105 : (−3)
x = 35
−30x − 24y = 54
−24y = 54 + 30x
−24y = 54 + 30 * 35
−24y = 54 + 1050
−24y = 1104
y = 1104 : (−24)
y = −46
Ответ: (35;−46)

$\begin{equation*} \begin{cases} 12x - 35y = 25 | * 2 &\\ -8x - 15y = -55 | * 3 & \end{cases} \end{equation*}$
$\begin{equation*} \begin{cases} 24x - 70y = 50 &\\ -24x - 45y = -165 & \end{cases} \end{equation*}$
24x − 70y − 24x − 45y = 50 − 165
−115y = −115
y = 1
12x − 35y = 25
12x = 25 + 35y
12x = 25 + 35 * 1
12x = 60
x = 60 : 12
x = 5
Ответ: (5;1)

$\begin{equation*} \begin{cases} 25x - 24y = -21 | * 2 &\\ 10x - 9y = 3 | * (-5) & \end{cases} \end{equation*}$
$\begin{equation*} \begin{cases} 50x - 48y = -42 &\\ -50x + 45y = -15 & \end{cases} \end{equation*}$
50x − 48y − 50x + 45y = −42 − 15
−3y = −57
y = −57 : (−3)
y = 19
10x − 9y = 3
10x = 3 + 9y
10x = 3 + 9 * 19
10x = 3 + 171
10x = 174
x = 174 : 10
x = 17,4
Ответ: (17,4;19)