PRE CAL HELP DON’T UNDERSTAND

You and a friend race across a field to a fence and back. your friend has a 50-meter head start. the equations shown represent you and your friend's distances dd (in meters) from the fence tt seconds after the race begins. find the time at which you catch up to your friend. you: d=∣−5t+100∣d=∣−5t+100∣ your friend: d=∣−313t+50∣∣

The sum of two numbers is 86, and their difference is 20. find the two numbers

Explain how you do each step what term makes it inconsistent y=2x - 4 ?