tolong no 7 dan 8. beserta caranya...

7][
Model matematika :
2 bilangan : x dan y
x + y = 31
x - y = 7

Jumlahkan
2x = 38 ---> x = 19
x + y = 31 ---> y = 31 - 19 = 12

8][
p = x + 5
l = x - 2
t = x

model matematika :
Panjang kawat yg dibutuhkan (k)
k = 4(p + l + t)
k = 4(x + 5 + x - 2 + x)
k = 4(3x + 3)
k = 12x + 12

k = 132
12x + 12 = 132
12x = 120
x = 10

Ukuran balok
p = x + 5 = 15 cm
l = x - 2 = 8 cm
t = x = 10 cm