1. The problem statement, all variables and given/known data A plastic pipe (k=0.092 W/m.K) of inner and outer radius of 1 and 1.25 cm, respectively. If the inner and outer surfaces are at 60 °C and 30 °C, respectively. The rate of heat transfer per unit length is close to: a) 98 W/m b) 89 W/m c) 78 W/m d) 168 W/m e) 112 W/m 2. Relevant equations Qk = ( Ti - To )/( ln| ro / ri | / 2π * k * l ) 3. The attempt at a solution I set up all of my given values into the heat transfer equation above but i am not given a length of the pipe.. Am i missing key information to finish this problem, or do i not need the length to solve? Also, I converted temps to Kelvin and the radii to meters.