The majority of automakers today call for oil changes at either 7,500 or 10,000 miles,
and the interval can go as high as 15,000 miles in some cars.
Yet this wasteful cycle continues largely because the automotive service industry,
while fully aware of the technological advances,
continues to preach the 3,000-mile gospel
as a way to keep the service bays busy.

The 3,000-mile oil change is "a marketing tactic
that dealers use to get you into the service bay on a regular basis
https://www.edmunds.com/car-news/tips-advice/stop-changing-your-oil.html

SAE 10W-30? SAE 5W-40? WHAT ARE THESE NUMBERS AND LETTERS?

 SAE (Society of Automotive Engineers) describe how well an oil flows (viscosity) through an engine
when the engine is cold in the morning and when the engine is warmed up .  
match this number to what is recommended in your vehicle owner’s manual.
Most motor oils today have two numbers (multi-viscosity): for example, SAE 10W-30.

The low number with the W (stands for Winter), or cold temperature number,
relates to how well the oil can be pumped or pushed through the engine at certain cold temperatures.

The second number (in this example 30) relates to how well the oil flows at higher engine temperatures..
Be careful, as higher or lower viscosity numbers may not be compatible with your engine.
To find out what oil grade is right for your engine, check your vehicle owner's manual.

WHEN DO I NEED AN OIL CHANGE? HOW DO I CHOOSE THE RIGHT TYPE OF OIL?
The timing of oil changes can vary, depending on the type of vehicle you drive, where you drive and how you drive.
Your vehicle manufacturer has done rigorous testing to help determine the timing between oil changes and the proper oil to use.
 All of this information can be found in your vehicle owner’s manual
https://www.jiffylube.com/resource-center/understanding-oil