yg tau tolong bantuin pke cara substitusi

1.) 3p = -q -10⇒ 3p + q = -10   (x3)  ⇒ 9p + 3q = -30
                           2p +3q = -16  (x1)  ⇒ 2p + 3q = -16
                                                             ____________ _
                                                               7p + 0 = -14
                                                                        p = -14/7
                                                                        p = -2
2.) 5x + 2y = 6 (x3) ⇒ 15x + 6y = 18
     4x + 3y = 2 (x2) ⇒  8x  + 6y = 4
                                   ____________ _
                                     7x + 0 = 14
                                              x = 14/7 = 2
     5x + 2y = 6
     5(2) +2y = 6
      10 + 2y = 6
               2y = 6 - 10
                2y = -4
                  y = -4/2 = -2
nilai x . y = 2 x (-2) = -4

3.) 3p + 7q = 1   (x-3)⇒ -9p -21q = -3
      2p - 3q = 16 (x7) ⇒  14p - 21q = 115
                                      ____________ _
                                        -23p + 0 = -115
                                                    p = -115/-23 = 5
        3p + 7q = 1
        3(5) + 7q = 1
         15 + 7q = 1
                  7q = 1 - 15
                  7q = -14
                    q = -14/7 = -2

 nilai pxq = 5 x (-2) = -10

4.) 3x1 + 4y1 = 7    (x3) ⇒ 9x1 + 12y1 = 21
     -2x1 + 3y1 = -16(x4) ⇒ -8x1 + 12y1 = -64
                                          _______________ _
                                              17x1 + 0 = 85
                                                        x1 = 85/17 = 5
      3x1 + 4y1 = 7
      3(5) + 4y1 = 7
       15 + 4y1 = 7
                4y1 = 7 - 15
                 4y1 = -8
                   y1 = -8/4 = -2
jadi nilai 2x1 - 7y1
              2(5) - 7(-2)
              = 10 + 14
              = 24