Easy problem with heat transfer from surrounding air to water tank

Hi!
Im doing some measures on a closed water tank with the water temperature 14C and surrounding air with temperature of 20C. I want to know how much heat transfer there is between the surrounding air and the tank.

A= 47m2 (area of tank in contact with the surrounding air)
Q=UA
U=1/(R1+R2+R3)

R1= air to tank transfer = 0.12 (i found this value)
R2= heat transfer in the tank material = d/λ. d=0.1 λ=1
R3= heat transfer between water and tank material. How do i calculate this?

Best regards / Jonas