Answer:
262 books sold
Step-by-step explanation:
This is a very vague word problem, but if it truly is just asking the amount of books sold (regardless of music or science), here's how to get the answer:
1. 287+134=421 - first you want to add together the two types of books to get the total amount of books in the store
2. 421-x=159 - create an equation and solve.
3. -x=-262 - follow order of operations and subtract 421 on both sides in order to isolate the variable
4. x=262 - divide each side by -1 to make the variable positive.
If you'd like an easier way, you can just:
1. 421-159=262 - it's easier, but my math teacher would count us wrong if we didn't do equations a specific way. Good luck!