Tolong jawab sama caranya

Dik :
Keliling = 80 cm
p = (2x – 3) cm
l = (x + 7) cm

Dit : nilai x?

Penyelesaian :
Keliling = 2 (p + l)
80 = 2 (2x – 3 + x + 7)
80 = 2 (3x + 4)
80 = 6x + 8
6x = 80 – 8
6x = 72
x = 72/6
x = 12 cm (C)