Hey there :) You'll have to use the formula of cylinder to get your answer :
Surface area of cylinder : 2(pi)(r^2) + 2(pi)(r)(h)
pi = 22.7 or 22/7
r (radius of cylinder) = 8 mm
h = height of cylinder = 20mm
●Hence, just substitute your answer in the given formula and also don't forget to check whether the answer required needs to be in mm or cm.
Hope it helps :)