I need help on 20 please and thank you

What is the difference between regular convex and concave polygons

At a sale this week, a desk is being sold for $213. this is a 29% discount from the original price. what is the original price?

1c) the number 131 is a term in the sequence defined by the explicit rule f(n)=5n-4. which term in the sequence is 131? 2a) write the first four terms of the function f(n)=n^2-1 2b) what is the 10th term of the sequence defined by the explicit rule f(n)=n^2-1 2c) the number 224 is a term in the sequence defined by the explicit rule f(n)=n^2-1. which term in the sequence is 224?