Copper balls (ρ = 8933 kg/m3, k = 401 W/m•°C, cp = 385 J/kg•°C, α = 1.166×10-4 m2/s) initi...

Copper balls (ρ = 8933 kg/m3, k = 401 W/m•°C, cp = 385 J/kg•°C, α = 1.166×10-4 m2/s) initially at 180°C are allowed to cool in air at 30°C for a period of 2 minutes. If the balls have a diameter of 2 cm and the heat transfer coefficient is 80 W/m2•°C, the center temperature of the balls at the end of cooling is

(a) 78°C 

(b) 95°C

(c) 118°C

(d) 134°C

(e) 151°C