A solid cylinder of radius r1 = 2.5cm, length h1 = 5.0 cm, emissivity 0.85, and temperature

Question:

A solid cylinder of radius r1 = 2.5cm, length h1 = 5.0 cm, emissivity 0.85, and temperature 30oC is suspended in an environment of temperature 50oC.
(a) What is the cylinder's net thermal radiation transfer rate P1?
(b) If the cylinder is stretched until its radius r2 = 0.50 cm, its net thermal radiation transfer rate becomes P2. What is the ratio P2/P1?