tolong bantu kerjain tugasku kak

11) 5(7x - 4) = - 3(-9x + 12) + 8
35x - 20 = 27x - 36 + 8
35x - 27x = - 28 + 20
8x = - 8
x = - 1
x = k = - 1
nilai k - 7 = - 1 - 7 = - 8 ( A )

12) y - y1 = m ( x - X1)
y - 3 = - 3 ( x + 2)
y = - 3x - 6 + 3
y = - 3x - 3
3x + y + 3 = 0 ( C )

13) A

14) misal
panjang = x
lebar = x - 12
K = 2 × ( p + l )
80 = 2 × ( x + x - 12)
80 ÷ 2 = 2x - 12
40 = 2x - 12
2x = 40 + 12
x = 52 ÷ 2
x = 26
jadi
panjang = x = 26
lebar = x - 12 = 26 - 12 = 14
Luas = p × l
= ( 26 × 14)
= 364 cm² ( C )

15) 5x² - 2xy - 8y - 6x² - xy + 3y²
= - x² - 3xy - 5y² ( B )

16) f(x) = 15 - 2x
f(b) = 15 - 2b
7 = 15 - 2b
7 - 15 = - 2b
- 8 = - 2b
b = 4 ( C )

17) 3x + 15 = 5x + 5
3x - 5x = 5 - 15
- 2x = - 10
x = 5
jadi panjang diagonal nya
= 3x + 15
= 3(5) + 15
= 15 + 15
= 30 m

18) x - 3y - 5 = 0
x - 3y = 5 |×2
2x - 5y = 9
maka
2x - 6y = 10
2x - 5y = 9
------------------(-)
- y = 1
y = - 1
subtitusi
x - 3y = 5
x - 3(-1) = 5
x + 3 = 5
x = 5 - 3
x = 2
nilai 3x + 2y
= 3(2) + 2(-1)
= 6 - 2
= 4 ( D )