Proportional relationships do you think that the number of heartbeats you can count is proportional to the number of seconds that you check your pulse ? /

The answer will be yes.

The heart beats at a fixed rate. The average heartbeat is about 72 per minute which is about 6 heartbeats in ever 5 seconds.

If we will count the number of heartbeats for more seconds, the number of beats will increase in proportion to the above rate. So increasing the number of seconds is increasing the number of heartbeats, thus, we can conclude that there is a direction proportion between the two quantities.  

The answer would be $68.04