5y² + 2xy – 20x - 100
Step-by-step explanation:
Assume that the distance between City A and City B is <em>x</em> miles,
& the speed of the plane from City A to B is<em> y </em>mph;
The return trip is 20 mph slower so the plane's speed is <em>(y – 20)</em> mph
Since <em>time = distance/speed;</em> The time taken by the plane from City A to B is <em>x / y</em> hrs.
The time taken in return flight is;
<em>x / (y - 20)</em> hrs
The layover was 5hrs long. Therefore the total time taken on the who return trip journey is;
x/y + x/(y-20) + 5
multiply each individual fraction with the LCM of the denominators
x(y-20) + xy + 5 y(y-20)
xy -20x +xy + 5y² – 100
5y² + 2xy – 20x - 100