Step-by-step explanation:
Using Charles law;
V1/T1 = V2/T2
Convert your temperatures to kelvin;
20+273=298k
60+273=333k
Then put the values the formula stated above
300/333 = V2/298
Make V2 the subject of the formula
V2= (300×298)/333
V2= 89400/333
V2= 268.47cm