Jawab:
[1.]  diagonal = 38 cm
[2]  Luas = 80 cm²
[3]  Luas = 289 cm²

Penjelasan dengan langkah-langkah:
[1.]  Diketahui
diagonal = (4x+2) cm dan (6x-16) cm
Ditanya panjang diagonal
4x+2 = 6x-16
6x-4x = 2+16
2x = 18
x = 18/2
x = 9
diagonal = (4(9)+2) cm = (36+2) cm = 38 cm

[2]  Diketahui persegi panjang
Keliling (K) = 36 cm, Lebar (l) = 8 cm
Ditanya luas (L)
K = 2(p+l)
p+l = K/2
p = (K/2) - l
Maka L = pl
L = ((K/2)-l)l
L = ((36/2)-8)8
L = (18-8)8
L = 10(8)
L = 80 cm²
Luas = 80 cm²

[3]  Diketahui persegi
Keliling (K) = 68 cm
Ditanya Luas (L)
K = 4s
s = K/4
s = 68/4
s = 17
Luas (L) = s² = 17² = 289 cm²

(xcvi)