step 1: get area av isos triangel with base=50 cm . . . angels=60 deg, hite= side*kosine(60 deg) or yukan yuze herons formuls . . . base=50, hite=43.30127, area=1082.53175 . . . step 2...Volume=leng*area=90*1082.53175=97427.8575 cc . . . step 3...liter=1000 cc, so volume=97.4278575 liters . . . or bout 97 liters