Each cone of the hourglass has a height of 18 millimeters . the total height of the sand within the top portion of the hour glass is 54 millimeters. the radius of both cylinder and cone is 8 millimeters. sand drips from the top to the bottom at a rate of 10n cublic millimeters per second. how many seconds will it take until all the sand has dripped to the bottom of the hour glass?

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

The correct answer would be in the photo below