<span>Mary ran the 5 kilometre race in 45 minutes. 45 minutes = 3/4 of an hour This means that her speed is S/t=5/(3/4)=20/3 = 6+2/3 (km / hour) </span><span>Melanie ran the 2 kilometre race in 17 minutes. </span><span>17 minutes = 17/60 of an hour </span><span>This means that her speed is </span>S/t=2/(17/60)=120/17= 7+1/17 <span>(km / hour) </span>So, Melanie is faster than Mary.
The width is 6 because you need to reverse what you would do to get 78. You would multiply length and width. Now you need to divide the area by length to find width.