Puzzle ZOIC 

Workings

Hint
How many minutes are between the times?

Answer
50 minutes.

Reasoning
If we call the number of unknown minutes T.

Between four o'clock and eight o'clock, there are 240 minutes.

There is some point between these two times, before which we have 3 lots of T, and after which we have one lot of T plus 40 minutes.

Therefore, in the 240 minutes, there are 4 lots of T plus 40 minutes.

   240 = 4 x T + 40.

Therefore, T = 50 minutes.