12-7 = 5cm
5:10 = 0.5cm.
8x0.5 = 4cm.
12+4= 16 (cm)
Answer: It turned out to be 16 cm long.
Equation: 1: let the candle be x cm per minute.
12+8x=7+ 18x
12+8x):(7+ 18x)= 1
x=0.5
12+8x= 16
2. Set the candle to be x cm long.
(X- 12):8=(X-7): 18
X= 16
Answer: It turned out to be 16 cm long.