Please assist me with this physics/chemistry question?

A certain mass of gas at 1000 degrees Celsius has a volume of 20.0 liters and a pressure of 1200 mm Hg. It is compressed to obtain a volume of 4.00 liters and a pressure of 3600 mm Hg. What is the final temperature?
1000°C = 1273K
Use combined gas equation:
P1V1 / T1 = P2V2/T2
1200*20.0/1273 = 3600*4.00/T2
T2*1200*20.0 = 1273*3600*4.00
T2 = 1273*3600*4.00 / 1200*20.0
T2 = 763.8K
Final temperature = 763.8K - 273 = 491°C

Note I always encourage my students to do a rough estimation of the magnitude of the answer;
Initial pressure * volume = 1200*20 = 24,000
Final pressure * volume = 3600*4 = 14,400
This shows that the final product is lower than the initial product . The final temperature must be lower than the original temperature. The answer I get seems to be correct.

Before compression: P₁ = 1200 mmHg, V₁ = 20.0 L, T₁ = (273 + 1000) K = 1273 K
After compression: P₂ = 3600 mmHg, V₂ = 4.00 L, T₂ = ? K

For a fixed amount of gas, P₁V₁/T₁ = P₂V₂/T₂
Then, T₂ = T₁ × (P₂/P₁) × (V₂/V₁)

Final temperature, T₂ = 1273 × (3600/1200) × (4.00/20.0) K = 7638 K
OR: Final temperature = (7638 - 273)°C = 7365°C