5. Tires should be replaced when

They are flat or get used a lot

Please mark brainlist if this helps!

Explanation:

I’m a mechanic.   You should replace your tires when you’re see a lot of cracking from being old.  About 6 years for good tires.  3 for cheap,ones.   or if you stand a Penney up in the tread and more than half is sticking out.  

the answer is b. ''a 12 cm 3 block of aluminum with a mass of 2 grams''.