cube quick formula

If you are using a computer, then
x^3=x*x*x

If you want to do it mentally, you can use the following formula:
(x+y)^3=x^3+3x^2y+3xy^2+y3

Try 34^^3=(30+4)^3;
x=30
y=4
30^3=27000
3*30^2*4=10800
3*30*4^2=1440
4^3=64
27000+10800+1440+64=39304

Otherwise use a calculator.