tolong bantu ngerjain soalnya nya pake cara

Mapel : Matematika
Bab : Sistem Persamaan Linear Dua Variabel (SPLDV)

2x + 3y = 8          | kali 3
3x + 5y = 14        | kali 2

6x + 9y = 24
6x + 10y = 28
-------------------   -
          -y = -4
           y = 4

2x + 3y = 8
2x + 3(4) = 8
2x + 12 = 8
2x = 8 - 12
2x = -4
x = -4/2
x = -2

x = a = -2
y = b = 4

4a - 3b = 4(-2) - 3(4)
4a - 3b = -8 - 12
4a - 3b = -20