An instructional video is 4.2 minutes long. how long is the video in seconds? how long is it in hours?

First we convert it in seconds.

Number of seconds in 1 minute = 60 seconds
Therefore,
Number of seconds in 4.2 minutes = 4.2 x 60 = 252 seconds.

Next we convert it in hours.

60 minutes make up an hour. So we can write,
Number of hours in 60 minutes = 1 hour
Number of hours in 1 minute = 1/60 hour
Number of hours in 4.2 minutes = 1/60 x 4.2 = 0.07 hour

Therefore, the video is 252 seconds or 0.07 hour long.