help please !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

volume tabung = phi.r^2.tomi
phi.r^2.t = 385 dm^3
22/7.r^2.100 dm = 385 dm^3
2200/7.r^2 = 385
2200.r^2 = 2695
r^2 = 2695/2200
r^2 = 1,31
r = akar 1,31
t = 1,15 dm = 11,5 cm