Aradio station broadcasts programs and commericals 20 hours everyday. the ratio of the time spent on commercials to the programming time is 1: 4. how much time each day does the station spend broadcasting commercials?

The answer is 4 hours

p - the programming time
c - time spent on commercials

A radio station broadcasts programs and commercials 20 hours everyday:
p + c = 20

The ratio of the time spent on commercials to the programming time is 1:4.
c : p = 1 : 4
p = c * 4 : 1
p = 4c

p + c = 20
p = 4c

4c + c = 20
5c  = 20
c  = 20 : 5
c = 4h