Aswimming pool is open for 7 1/2 hours during a day. the pool keeps one lifeguard on duty at a time, and each lifeguard's shift is 1 1/2 hours long.

You will need 5 lifeguards a day

There are 5 shifts because 7 1/2 divided by 1 1/2 equals 5.

Skew lines(segments) are lines(segments) in 3 dimensions that do not intersect the given segment and are not parallel to it.  ae, bf, eg, and fh are your skew segments.  i hope that : )