Ok, to check back on what the measure of a radian is, it is 57.3 degrees. So it would be about .78

radians
Let
Vco------------------- >Volume cone
Vcy------------------ >Volume cylinder
r= 8mm
hco----------- > height of cone=18 mm
hcy------------ > height of cylinder =54-18=36 mm
then
Vco=π*r² *hco/3--------- > π*8² *18/3=π*384 mm³
Vcy=π*r² *hcy--------- > π*8² *36=π*2304 mm³
the total cubic millimeters of sand=Vco+Vcy=π*384+π*2304=π*2688
if 10π cubic millimeters --------------------- > 1 seg
π*2688--------------------------------- X
X=π*2688/10π=268.8 seg
the answer is 268.8 seg
85/100 and in simple terms 17/20