On a typical day flights at a local airport arrive at a rate of 10 every 15 minutes at this rate how many flights would you expect to arrive in one hour

40 flights, you could use rates in this situation. 
15 min*4=60 min=1 hr
10:15 multiply each side by 4
40 flights:60 minutes

Ifound this on google “that means that the graph of a function with direct variation has these features: it is a straight line: because the slope is the ratio y/x = k. it passes through the origin (0,0): because y = kx = k (0) = 0.” i hope this you for what your looking for