5x10^-4 X 3.5 X 120 = ?

5*10^(-4)*3.5*120 = 0.21     via Web2.0 calculator

Or you could do it without a calculator    

\(5*10^{-4}*3.5*120\\ =5*7*60*10^{-4}\\ =7*300*10^{-4}\\ =2100*10^{-4}\\ =0.21 \)