Cara plus jawaban kak no 7 11 12

7. keliling = 2(p×l) = 32
p+l = 16
4x-3 + 2x+1 = 16
6x = 18
x = 3

luas = 9 × 7 = 63 cm^2

11.
[tex] {( - 3)}^{k + 1} .7. {3}^{ - k} \\ { - 3}^{k} . { - 3}.7. \frac{1}{ {3}^{k} } \\ - 21[/tex]
12. 50