The convection coefficient for flow over a solid sphere may be determined by submerging the sphere, which is initially at 25 °c, into the flow, which is at 75 °c, and measuring its surface temperature at some time during the transient heating process. if the sphere has a diameter of 0.1 m, a thermal conductivity of 22 w/(m·k), and a thermal diffusivity of 9.0 ×10-5 m2/s, at what time will a surface temperature of 60 ºc be recorded if the convection coefficient is 300 w/(m2·k)?