How many seconds are there in 7 days?

Explanation

1Day = 24hr, `1 = (24h)/(1day) , 1hr = 60min`,
1 = `(60min)/(1hr) , 1min = 60sec , 1 = (60s)/(1min)`
The unit factors can be multiplied in series in one step only.
`7 Day xx (24h)/(1day) xx (60min)/(1min) xx (60s)/(1min) = 7xx24xx60xx60s = 604800s`